You have the German 4 Layer Mobo I think. There is probably a Jumper that you can set to change from 512K to 1MB Chip. You must have an 8372A Agnus in there at least. You could use the 8372B (I think) but you would still only be able to address 1MB of chip.
You would need to find a Mega-CHIP or TOP-CHIP 2MB Chip upgrade, (Just sits in the agnus socket). Those are hard to come by. I just paid an arm and a leg for one. You should certainly get the 1MB Chip going though. It's odd because both my A2000's were 1MB chip as standard. Must be the German Mobo. There are documents on the net that will explain the Jumpers for you. Just do some googling.
If you have an 8371 Agnus, then replace it with an 8372A at least, or you cannot go to 1MB Chip.
Oh and if your going to remove the Agnus, make sure you get a PLCC chip puller, or you WILL break the socket for sure.
Good luck :-)