http://www.kv32tweak.freeuk.com/
Click on Service Menu at the top for a fuller description, but basically
Turn the set on with the televisions on/off switch.
Turn the set off from the remote control.
Press the [I +] button.
Press the [5] button.
Press the [Vol +] button.
Press the [TV] button.
When the TV comes on, press the MENU button on the remote and you'll get a list of options, one of which is for geometry (I'm at work at the moment, so I'm afraid I can't remember the exact menu options).
As usual, proceed with extreme caution and make a note of all the settings before changing them.