need help upgrading mac G4

[horsegal]

My mac G4 says the start up disc is too full and I need to dump. I have dumped all I can, I make catalogs for my business have lots of jpegs etc. Use huge programs to do this with. Can I upgrade to a larger memory or what on this? Any suggestions on what to do and where to go to do it would be helpful.
Mac G4 800 Mghz half bowling ball Imac model.

[yellow]

You should just invest in an external hard drive. It also sounds like you don't have a backup solution. That's begging for trouble.