How to remove your Last.fm account
From the Last.fm faq: Should you wish to permanently delete your account, you can do this on the Data tab (https://www.last.fm/settings/account) in your settings. From here, make sure you enter your password correctly, and confirm that you want to delete your account.
Direct removal link: https://www.last.fm/settings/account
Helpful Trick: Removing online data
Publicly visible text/images often aren’t properly removed even when you succeed in removing an account. Try editing or removing them manually before removing the account itself. If you’re unsure what happens to your tracks: this can be found mostly in the Terms of Service/Privacy Policy; otherwise you can always contact Last.fm and ask personally. By the way, removal requests don’t necessarily mean your data will actually be removed (e.g. due to legal obligations).
Helpful Trick: Remove third-party logins
If you signed up for Last.fm using a third-party login such as Facebook or Twitter, you probably want to revoke all access from Last.fm. Click here to find out how.