iMac G4 memory upgrade

I have an old model of an iMac G4. I would like to upgrade the memory. Does anyone know where I can buy more memory? Is this something I can do myself or do I need to take it in to the Apple Store?
Thanks!
P.S. Assume I am computer illiterate when answering this!

The G4 iMacs took different types of memory depending on the model. The earlier ones (700-800 MHz) have a single PC133 SO-DIMM slot. The 1 GHz and 1.25 GHz versions have a single PC2700 DDR SO-DIMM slot.

On top of that, all iMac G4s had a factory-accessible DIMM slot that took the same kind of memory as the user slot, but in DIMM (not SO-DIMM) form. It's harder to access but it's possible to upgrade that slot as well if you wish. If you are computer illiterate, I would just forget about this slot.

For reference, DIMMs and SO-DIMMs are different types of memory modules. They do the same thing but SO-DIMMs are more compact and are meant for use in laptops and some smaller desktops (like the iMac).

Anyway, if you have a 700-800 MHz model, you should get this one. If you have a 1-1.25 GHz model, you should get this one.

Thanks so much!