Once you receive a notification from Spotify that lossless is available, you can use the Spotify app to enable the feature. To do this, tap on your profile image, go to Settings & Privacy, then Media ...

To export Audacity files as MP3s, you just need to use the "Export" option in the program's "File" menu. Older versions of Audacity can't export MP3s natively, and you'll need to install an add-on ...