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Before you upgrade always, Always, ALWAYS BACKUP YOUR WEBSITE!
If your core XOOPS is 2.4.1 without any hacks applied then simply overwrite your current installation with the 2.4.1 to 2.4.2 patch. The patch only includes the few files that have changed or are new. If you have applied hacks then you'll need to search though the patch to identify any hacks that will be overwritten.
Good luck :)