You'll need to adjust the jumper settings. Actually
they're not jumpers but solder pads so you need
to move the solder blob from one to another.
There are 3 pads in total that may need to be changed.
IIRC this is all documented in the schematics.
There should be one called CE and you move this to 1M
instead of the 256k, and there is A16 and A17 that may
need to be changed. If you need help I'll dig
out the schematics.