How to extend Disk in VXVM

HI,

I have 1 Lun with size 120GB, on that LUN we have 1 Disk group with 4 DB volume, now i want to extend the size of "DISK" not DG nor Volume.Can i extend Disk size from 120 G B to 200 GB???

If yes, thn please share POA also...

Thanks in Advance...