Ugrading 10.3.9 in G4 (933) Quick Silver

Hi.

I am using a Apple Powermac G4 933Mhz (Quicksilver) and running OS 10.3.9. I would like to know if this can be upgraded to any later version and if so what the last version that can be installed in this system and how to do this?

Also, I am currently using 512MB x 2 RAM. Whats the maximum RAM that this system can support? Can I remove this and imnstall 2 x 2 GB to give me 4 GB RAM?

Dilip Param