First of all you need to add the LUN to the disk group
# vxdisksetup -if <disk name> --> This will initialize the disk. Basically it will put private and public region on the disk header so that volume manager can work with the disk.
# vxdg -g <disk group name> adddisk <disk access name, as you prefer>=<disk media name, as displayed in "vxdisk list" command>
This command would increase the volume size as well as file system size
# vxresize -g <disk group name> -F vxfs <volume name> <specify new volume size>
FYI. VM4.0 is no longer supported, unless you have support exception, so I suggest you to go for an upgrade if it is an important server.