On the R24, you have the option to change the BPM or stretch the files. It's around page 60 in the R24 manual. The same function isn't found on the R16, since it doesn't have rhythm patterns.
If you are simply trying to adjust the whole song for a final release, you could mix down the song, then export it to a DAW like Reaper, where you can change the BPM easily, and also adjust pitch as needed. If you want to do it inside the R16, you could record the tracks, import each into the DAW, adjust the pitch, then import them back into the R16 project. It's a bit of a hassle but it should work.
