How can I update iMac PowerMac4.2 PowerPC G4 Firmware and Upgrading to Mac OS X 10.3.9

Question

Trying to save this old iMac

Answer 1

Greetings:
This link:
http://support.apple.com/kb/DL496
will get you the 10.3.9 combo updater that will update any versions of 10.3 to 10.3.9 assuming you already have some version of 10.3 installed.
Apple has dropped a lot older reference material for its older computers from its site (Grrr!). However, the MacTracker database doesn't show that any firmware updates were issued for the G4 iMacs.
As for as upgrading hardware, there is not a lot you can due yourself because the design of the G4 discourages end-users from opening it up. You can get it open but, without proper reassembly expertise, the computer will overheat and die.
RAM upgrades are affected by this design. The G4 iMac has two RAM slots but only one is accessible to the average user. That makes it hard to max out the RAM. That model can hold up to one 512MB module in each slot for a total of 1GB RAM. Most people has to satisfy themselves with putting a 512MB module i the "user accessible" slot and simply live with what was in the "factory" slot, often a 256MB module.
Upgrading the hard drive faces the same take-apart limitations as accessing the internal RAM slot. Not a typical DIY event.