If you have a standard Amiga 500, they come with 512KB of RAM standard on the motherboard. By adding an additional 512KB of RAM to the trapdoor slot (such as our expansion board), you will have a total of 1MB of RAM.  The memory however will most likely show up as 512KB or Graphics or CHIP memory, and 512KB of additional memory unless your Amiga 500 has been previously modified to address it all a CHIP RAM.

It is possible to convert the additional 512KB to CHIP RAM provided you have the correct “Fat Agnus” chip on your motherboard, and jumper modifications.  The modifications you’ll need to do vary on what revision motherboard is installed in your Amiga 500.

This PDF in the link below is an excellent guide that will explain what you need and how to do it on both revisions:
Xform-A500

This is also a great youtube video describing how to perform the upgrade: https://www.youtube.com/watch?v=AwL4T9LCruk