Expand the CLARiiON LUN on the ClaRiiON storage system to the desired LUN size, issue a rescan at the ESX level. Sometimes you have to rescan again before your metalun will be shown.(I have to find out why) Your old disk will disappear from storage adapter view and the new metalun wil be shown.
Switch over to the Storage view:
Right click your storage disk what needs to be increased. Select properties…
Hit the Increase button:
Select the volume you need:
Now you have to expand your disk within the properties of the VM.
The Last step go on the the console of your VM do a rescan of your disks and extend your disk on OS level.