You don't need to worry about any of the PRX stuff unless you want to get the PS1 emulator from previous custom firmwares, which is mostly unnecessary because 3.52 M33-4 has a very good PS1 emulator. To update, you just copy the updater to the GAME150 folder and run the app. It's that simple.

However, you don't need to do the updates in order - you can leap from 3.52 M33 to 3.52 M33-4 without doing any of the ones in between, as the 3.52 M33-4 update includes all the updates from 3.52 M33-2 and 3.

And a PRX is a system file, like DLLs but for the PSP.

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