I have a Ubuntu 12.04 VM running on VMWares ESXi 5.1.

The server (VM) itself has run out of space, the results of df -h are as follows:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        19G   17G  1.2G  94% /
udev            490M  4.0K  490M   1% /dev
tmpfs           200M  232K  199M   1% /run
none            5.0M     0  5.0M   0% /run/lock
none            498M     0  498M   0% /run/shm

The original VM HDD size was just under 19GB which is I have now increased to 100GB within the vCenter GUI:

Is there a simple way of doing this? The VM doesn't seem to acknowledge the increase at all.