If you are using a seriously old version of Audacity, the Export dialog will not say that. You will need to change the export bitrate in Audacity Preferences, but before you do that, Save the Project and Export a WAV of the work and upgrade to the latest Audacity. Sooner or later, the older, unstable Audacity is going to do something evil and destroy your show.
We would also warn that you can’t open your existing MP3 and export it at a higher bitrate. that will be rejected because of excessive compression bubbling, honking sound damage. You need to start with a WAV or AIFF export or the original Audacity Project. MP3 is not a good archival format. Use Microsoft WAV or AIFF (Apple Uncompressed).
Microsoft WAV is the Audacity default because it will open in all three computer platforms.
Koz