How to Cancel YouTube Music Premium
Quick answer
Go to youtube.com/paid_memberships, click Deactivate, then Continue to cancel and confirm (Google's steps). Your benefits last until the end of the billing period.
Before you cancel
Downloads stop working once Premium ends, and on the free tier YouTube Music plays ads and limits background play. Your playlists stay. If you're switching services, move them now.
Pick where your music is going.
By how you pay
youtube.com/paid_memberships > Deactivate > Continue to cancel > pick a reason > Yes, cancel.
If you joined in the iPhone app, cancel in your Apple account: Settings > your name > Subscriptions.
Cancel in the Play Store under Payments & subscriptions.
Pause instead
YouTube lets you pause instead of cancelling. Billing restarts on its own when the pause ends, so set a reminder if you don't want that.
FAQ
Yes. YouTube Music Premium is part of YouTube Premium, so both end together.
No. They stay on your Google account and still play on the free tier.