Ram Upgrade for PowerBook G4

not sure on apple what can be removed and not removed etc.

I have a PowerBook G4 w/1.33 GHz, and Ram is as listed.

Dimmo/Built-in 256 MB
Dimm1/j31 512 MB DDR SDRAM PC2700U-25330

What can I bump this up to and can the built-in be swapped out as well ?

I know this may be a really dumb question but it is one i just don't know the answer too.

thanks !