The standard location for the ACC button is fine if your car is a left hand drive but not so great for us in the UK as you can't see very well if your in 1st or 3rd gear. So it's quite handy to move it to the right so that you can get to it and see very easily.
Use the trim tool to level up the gear gaiter surround and pull it up to reveal two torx bolts. Un-screw these and lift up and pull out the storage tray/ashtray unit.
Disconnect the ACC button from it's cable and pop it out of the housing. Beware of the metal clips these can easily fall off (they aren't hard to put back on but make sure you don't loose them).
In order to get the ACC button to fit you need to shave a plastic fin off of it using a stanley knife as each button in this row is designed to go into only one specific slot. This is dead easy but be careful you don't cut yourself.
Now simply do the steps in reverse to put everything back together again and you're all done.