All you need to do is purchase a copy of 10.4 (Tiger) and run the installer.
It really is as simple as that.
System 9.2.2 will remain on your drive and the system will launch System 9 (Classic) when it needs it.
If you need to boot into System 9 by itself, go to the System Preferences > Startup Disk and select the System 9 disk that appears in the choices.
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Please help. Can't seem to find the answer to this anywhere. I have a G4 running 9.2.2 and 10.1.3. I want to upgrade the 10.1.3 to 10.4 Tiger without nuking 9.2.2. How do I do this? Several years ago when I was into messing with my computer I upgraded my 9.0 to 9.2.2 and then added the 10.1.3. I don't remember how I did this. The drive is not partitioned because I can't select a volume at start startup. If I press the option key at startup I see only the volume I shutdown in. If I want to switch between the 2 operating systems I have to select the 9 in 10 or vice versa except if I shutdown in 9 upon starting up again if I press the X key I get OS X. I have recently updated the firmware. Any help would be greatly appreciated. Thank you

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