I would get P3DO Explorer. It's free and it can convert rsr to png or png to rsr. I bought the pro version for somewhere around $25 but to start with, the free version works great. And you can set it to delete the original files after conversion so you don't have all those RSR you don't need. The pro version lets you browse subfolders which makes the job faster but even the free version can convert all files in one folder.

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