I think that option on the menus was dropped a few versions ago. There is a file in the RealTracks folder called DECOMPRESS. If you click on that, it will convert all files in the Realtracks and subfolders to WAV. The same file should also be in your RealDrums folder.

Be advised that it will convert ALL .wma files that it finds. If you want a few, copy the Decompress to any folder(s) and run it from there.

R