As an obvious novice I want to know how to upgrade my mac mini OSx 10.4 to a newer system can anyone help?

Choose About this Mac from the Apple menu and check the processor.

If it's a G4, buy a retail Mac OS X 10.5 DVD from a source such as Amazon or eBay; Apple still might have copies in stock if you phone them.

If it's an Intel Mac, buy a Mac OS X 10.6 DVD from the online Apple Store.

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At the Apple Icon at top left>About this Mac.

Then click on More Info>Hardware and report this upto but not including the Serial#...

Hardware Overview:

Machine Name: Mac mini

Machine Model: PowerMac10,1

CPU Type: PowerPC G4 (1.2)

Number Of CPUs: 1

CPU Speed: 1.42 GHz

L2 Cache (per CPU): 512 KB

Memory: 512 MB

Bus Speed: 167 MHz

Boot ROM Version: 4.8.9f1

And if you have a Core2Duo Mac Mini, while you can upgrade to 10.7 or later, you'll lose access to certain applications.

If the computer has a power pc processor, the furthest you can go is to OSX 10.5. To do this, you will have to get a update disk from amazon or eBay. as 10.6 lose support for power pc, you cant update to that. Whereas, if it is a intel processor, you can go to at least 10.6, using the update disks, maybe more, some can be updated to 10.7, but if you do this, it will seriously impact the performance. I recommend that you buy a new computer, as any computer that old is obsolete, and it will not be great, even if updated. As the newest system is 10.9, so even if you update, it is still out of date, so it may not be worth the trouble.

Its a shame that computers age so quickly...