It's the thing which the belt is hanging off at the moment. Nothing needs to come off. Might be easier with the front end jacked up though. You need to work underneath. It is actually 1 bolt which goes through a nut. It is in the bottom left hand corner of your second picture.
 
dont need many tools, think its just a 16 or 17mm spanner, 13mm spanner and an allen key and can push the power steering pump inwards to swap the belts.
 
A good set of spanners 8mm-21mm inclusive will be good for general work. A 1/2" or 3/8" socket set covering the same would also be good. After that things like a selection of screwdrivers and allen keys.
 
21mm spanner is the holy grail of tools. i desperately need one but strapon want 25 quid for one.