Thats actually not easy to describe, without photos or diagrams etc, but basicly the front of the seat squab (thats the lower part) needs to be pushed down and back to release it from its retaining clip. For a first timer it can be very frustrating. However an easier way is to pull the back of the seat squab up, that means puting your fingers between the backrest and the lower part and pull the lower part up and forward till it comes out past the backrest, then if you grab the front of the seat and wriggle it it should come out. Do the same for the other side. Be carefull though cos the back of the lower part has some sharp bits of wire in it and you can damage the seat if your not carefull. The backrest is held in place by a 10mm bolt down near the seat belt bolts. It comes out in two pieces, just take out the bolt then slide the backrest up.
Gees I'm not sure if I've described that very well, if anyone else can make it clearer, feel free to jump in.
Anyway, good luck ducatis
Mike