You need to set the Jumper 1 for the size of ram fitted. See picture here
http://amiga.resource.cx/photos/a2091 the Jumper is on the top edge just in front of the 2 chips with labels stuck on them.
The ram chips are fitted in columns from the inside of the board outwards. 1st row = 512k, 1st and 2nd = 1Meg, all 4 columns full = 2Meg.
Hope that helps, Dave G 8-)
