I think you need to swap out an Amiga chip and run some wires around the board to get an A500 or A2000 to more then 1MB CHIP RAM. The A500 has some inexpensive side cars with 2MB fast RAM if you can find them (the sidecar is a Zorro 2 connector). Why do you need the extra RAM anyway, 1MB is fine for most games and apps that a 68000 would be good for.
Also if you swap out the battery on the A501 with a coin type (I did that to mine), make sure you have a diode in line with the + lead because the old battery is a rechargable one and a coin type can blow up if not protected from charging.