Steps:

Warning! The data on that partition will be lost and no other effect on the disk.

There is no as such process to delete the partition, but you can follow this steps to cleat it and resize it as per your requirement.

1. Format
2. Select the disk
3. Select partition menu
4. Select the slice you need to clear
5. Bypass all the options with out any argumets exept the option it asking for size to enter, at this point give 0 (zero) as the argumet (very important).
6. After this label the disk -- very important and then check the partition table you can see the partition size is zero.
7. Then you can reselect the slice and you can follow the normal steps and give the new space and atlast label the disk.

Sample procedure (Repeat the following as per your requirements):

	# format 
	Searching for disks...done


	AVAILABLE DISK SELECTIONS:
		   0. c1t0d0 <GNU Parted Custom cyl 8924 alt 0 hd 255 sec 63>
			  /pci@1f,700000/scsi@2/sd@0,0
		   1. c1t1d0 <SUN72G cyl 14087 alt 2 hd 24 sec 424>
			  /pci@1f,700000/scsi@2/sd@1,0
		   2. c1t2d0 <SUN72G cyl 14087 alt 2 hd 24 sec 424>
			  /pci@1f,700000/scsi@2/sd@2,0
		   3. c1t3d0 <SUN72G cyl 14087 alt 2 hd 24 sec 424>
			  /pci@1f,700000/scsi@2/sd@3,0
	Specify disk (enter its number): 1
	selecting c1t1d0
	[disk formatted]

	FORMAT MENU:
			disk       - select a disk
			type       - select (define) a disk type
			partition  - select (define) a partition table
			current    - describe the current disk
			format     - format and analyze the disk
			repair     - repair a defective sector
			label      - write label to the disk
			analyze    - surface analysis
			defect     - defect list management
			backup     - search for backup labels
			verify     - read and display labels
			save       - save new disk/partition definitions
			inquiry    - show vendor, product and revision
			volname    - set 8-character volume name
			!<cmd>     - execute <cmd>, then return
			quit
	format> p

	PARTITION MENU:
			0      - change `0' partition
			1      - change `1' partition
			2      - change `2' partition
			3      - change `3' partition
			4      - change `4' partition
			5      - change `5' partition
			6      - change `6' partition
			7      - change `7' partition
			select - select a predefined table
			modify - modify a predefined partition table
			name   - name the current table
			print  - display the current table
			label  - write partition map and label to the disk
			!<cmd> - execute <cmd>, then return
			quit
	partition> p
	Current partition table (original):
	Total disk cylinders available: 14087 + 2 (reserved cylinders)

	Part      Tag    Flag     Cylinders         Size            Blocks
	  0 unassigned    wu       0                0         (0/0/0)             0
	  1 unassigned    wu       0                0         (0/0/0)             0
	  2     backup    wm       0 - 14086       68.35GB    (14087/0/0) 143349312
	  3 unassigned    wu       0                0         (0/0/0)             0
	  4 unassigned    wu       0                0         (0/0/0)             0
	  5 unassigned    wu       0                0         (0/0/0)             0
	  6 unassigned    wm       0 - 14079       68.32GB    (14080/0/0) 143278080
	  7 unassigned    wm   14080 - 14086       34.78MB    (7/0/0)         71232
	  
	partition> 2
	Part      Tag    Flag     Cylinders         Size            Blocks
	  2     backup    wm       0 - 14086       68.35GB    (14087/0/0) 143349312

	Enter partition id tag[backup]: unassigned
	Enter partition permission flags[wm]: 
	Enter new starting cyl[0]: 
	Enter partition size[143349312b, 14087c, 14086e, 69994.78mb, 68.35gb]: 0
	
	partition> 6
	Part      Tag    Flag     Cylinders         Size            Blocks
	  6 unassigned    wm       0 - 14079       68.32GB    (14080/0/0) 143278080

	Enter partition id tag[unassigned]: 
	Enter partition permission flags[wm]: 
	Enter new starting cyl[0]: 
	Enter partition size[143278080b, 14080c, 14079e, 69960.00mb, 68.32gb]: 0

	partition> 7
	Part      Tag    Flag     Cylinders         Size            Blocks
	  7 unassigned    wm   14080 - 14086       34.78MB    (7/0/0) 71232

	Enter partition id tag[unassigned]: 
	Enter partition permission flags[wm]: 
	Enter new starting cyl[14080]: 0
	Enter partition size[71232b, 7c, 6e, 34.78mb, 0.03gb]: 0

	partition> p
	Current partition table (unnamed):
	Total disk cylinders available: 14087 + 2 (reserved cylinders)

	Part      Tag    Flag     Cylinders     Size            Blocks
	  0 unassigned    wu       0            0         (0/0/0) 0
	  1 unassigned    wu       0            0         (0/0/0) 0
	  2 unassigned    wm       0            0         (0/0/0) 0
	  3 unassigned    wu       0            0         (0/0/0) 0
	  4 unassigned    wu       0            0         (0/0/0) 0
	  5 unassigned    wu       0            0         (0/0/0) 0
	  6 unassigned    wm       0            0         (0/0/0) 0
	  7 unassigned    wm       0            0         (0/0/0) 0

	partition> 0
	Part      Tag    Flag     Cylinders     Size            Blocks
	  0 unassigned    wu       0            0         (0/0/0) 0

	Enter partition id tag[unassigned]: 
	Enter partition permission flags[wu]: 
	Enter new starting cyl[0]: 
	Enter partition size[0b, 0c, 0e, 0.00mb, 0.00gb]: 14087c
	partition> p
	Current partition table (unnamed):
	Total disk cylinders available: 14087 + 2 (reserved cylinders)

	Part      Tag    Flag     Cylinders         Size            Blocks
	  0 unassigned    wu       0 - 14086       68.35GB    (14087/0/0) 143349312
	  1 unassigned    wu       0                0         (0/0/0)             0
	  2 unassigned    wm       0                0         (0/0/0)             0
	  3 unassigned    wu       0                0         (0/0/0)             0
	  4 unassigned    wu       0                0         (0/0/0)             0
	  5 unassigned    wu       0                0         (0/0/0)             0
	  6 unassigned    wm       0                0         (0/0/0)             0
	  7 unassigned    wm       0                0         (0/0/0)             0

	partition> label
	Ready to label disk, continue? y

	partition> q
	
	format> q

Create the pool:

	# zpool create data raidz1 c1t1d0 c1t2d0 c1t3d0

Verify:

	# zpool status
	  pool: data
	 state: ONLINE
	 scrub: none requested
	config:

			NAME        STATE     READ WRITE CKSUM
			data        ONLINE       0     0     0
			  raidz1    ONLINE       0     0     0
				c1t1d0  ONLINE       0     0     0
				c1t2d0  ONLINE       0     0     0
				c1t3d0  ONLINE       0     0     0

	errors: No known data errors	

	# df -h
	Filesystem             size   used  avail capacity  Mounted on
	/dev/dsk/c1t0d0s0       60G   4.6G    55G     8%    /
	/devices                 0K     0K     0K     0%    /devices
	ctfs                     0K     0K     0K     0%    /system/contract
	proc                     0K     0K     0K     0%    /proc
	mnttab                   0K     0K     0K     0%    /etc/mnttab
	swap                    14G   1.4M    14G     1%    /etc/svc/volatile
	objfs                    0K     0K     0K     0%    /system/object
	sharefs                  0K     0K     0K     0%    /etc/dfs/sharetab
	/platform/sun4u-us3/lib/libc_psr/libc_psr_hwcap1.so.1
							60G   4.6G    55G     8%    /platform/sun4u-us3/lib/libc_psr.so.1
	/platform/sun4u-us3/lib/sparcv9/libc_psr/libc_psr_hwcap1.so.1
							60G   4.6G    55G     8%    /platform/sun4u-us3/lib/sparcv9/libc_psr.so.1
	fd                       0K     0K     0K     0%    /dev/fd
	swap                    14G   104K    14G     1%    /tmp
	swap                    14G    32K    14G     1%    /var/run
	data                   134G    21M   134G     1%    /data

Reference:
http://southbrain.com