where do I go to transpose song to different keys
If you wish to retain the original tempo, use the “Change Pitch” effect. Note that this effect will have an impact on the sound quality - the greater the pitch shift the greater the impact on sound quality. For best quality, try both with and without “Use high quality stretching (slow)” selected to see which sounds better (Usually it sounds better with that option selected, but not always - it depends on the source material). https://manual.audacityteam.org/man/change_pitch.html
Alternatively, if you don’t mind the tempo changing, then the “Change Speed” effect may give better sound quality: https://manual.audacityteam.org/man/change_speed.html
And stay away from MP3. MP3 creates sound damage every time you make one and you can’t stop it. Use WAV (Microsoft) 16-bit.
You suggest 16 bit wav. I’m set for 24 bit. Isn’t that better? The slower transposition is much better quality, IMO.