Upgrade HTC sensation Gingerbread to Ice Cream Sandwitch
Upgrade HTC sensation from Gingerbread to Ice Cream need several step to avoid HTC sensation or HTC sensation XE become brick.
The device s-off
Read here how to make HTC sensation become S-Off (security off). Rooting or flashing can not do if HTC still in S-ON.
The CID Number device
HTC Sensation CID and MID number is another thing that you must know, upgrade from gingerbread to ice cream sandwich (ICS) need a correct firmware. Read here to find out the HTC Sensation CID and MID number
Flashing Using firmware that match with Sensation CID Number
Using custom firmware with correct version will avoid your HTC become brick after flashing with new custom ROM. Download the custom firmware that support for ICS upgrade here.
After you got to flashing your HTC sensation, read Flashing HTC Sensation Firmware
Flashing ROM Ice Cream Sandwitch
There some custom ROM that already based on ICS, just pick up one then Flash your HTC using that ROM. Here`s some custom ROM for HTC Sensation
Do With Your Own Risk