To cancel Spotify Premium, log in at spotify.com in a browser, open Account, choose Manage your plan, and click Cancel Premium.
The catch most people hit: you can't cancel Premium from inside the mobile app.
Deletion is permanent, so Spotify makes you confirm it deliberately.
This trips up more people than any other part of the process.
This is the part people regret skipping.
Read the complete breakdown, fixes and what happens next.