If you want to upload your audio recording to a podcast host, you may need an MP3 file.
You can use Riverside's Editor to export your recording and select either an MP3 or WAV file on the export options panel.
To convert audio files that you did not create on Riverside or that you edited in desktop editing software, use a program like Audacity. Learn more about exporting files with Audacity. This article explains more about how to convert audio files: How to Convert WAV to MP3 in Audacity.