What badges have you got? The whole trim pieces (eg the front with the chrome bit) or just the actual round bit with the alfa logo? If it's the proper ones:
Front badge: It's glued and bolted onto the bonnet, just open it and look on the other side of the badge. Undo it and prize it off. Stick new one one, rescrew, easy.
Rear badge: On early cars are screwed on from behind. You have to remove the black trim piece from the tailgate to gain access. It's just a few screws and the thing will prize off. Later cars the whole thing is glued on. Try warm water and some dental floss to slice through the adhesive. Clean up the area with alcohol or something so the new one sticks on well.
Steering wheel... no idea... I assume it's just one that sticks over the original badge? I wouldn't fancy prising away at the badge in case I wrecked the wheel.