Here's the sequence for changing a vserver LVM partition size
vgdisplay
vserver NAME stop
umount /dev/my_volume_group/NAME
e2fsadm -L [NumberOfGigabytes]G /dev/my_volume_group/NAME
If this command isn't present or doesn't work use these commands
lvextend -L+[NumberOfGigabytes]G /dev/my_volume_group/NAME e2fsck -f /dev/my_volume_group/NAME resize2fs /dev/my_volume_group/NAME
mount /dev/my_volume_group/NAME /vservers/NAME
vserver NAME start