Audacity is open-source sound recording and editing software that produces files with the extension AUP. These files can be converted within the Audacity program. This can be confusing if you have not used the software before, but converting to MP3 is not a difficult process.
Download and install Audacity.
Run Audacity and open the AUP file you would like to convert. Click "File," then "Open" and choose the file.
Click "File," then click "Export as MP3."
Rename your file so you can differentiate it from your original AUP file.
Click "OK" to start the conversion process. Your AUP file should convert to an MP3.
You can also convert AUP to MP3 files using Goldwave converter. This is, however, not a free application.