Ya, can't help you there... that Tutorial seems to be from another Forum so best to ask them since they made it. I told you how I would do it above... open the iSO in UMDGen v2.01, then make any necessary changes (swap PRX, etc) and save- That's what I do here. If you try my method and get stuck, then post back with specifically where you are stuck and we'll try to help ya.
As for the link you posted from UMDGen, that is a dated Tutorial also... telling you to drag the files in, etc. With the newer UMDGen versions you don't have to do that.