How to add song from Spotify so you can adjust tempo.
Use a Spotify Music Converter to remove the digital protection from Spotify songs first. Then download Spotify songs as local files. Finally, you can adjust the tempo. I use AudKit to get this goal.
You need to remove DRM from Spotify firstly,use some tools like Spotify music to mp3 converter /Spotify music downloader etc.then use the methods from Kelesy. Audacity is useful.