Deleting a MySpace account is a bit convoluted, but doable. You’ll need to login to your account and then go to the “My Account” link, and then select “Account”. Scroll until you see the “Account Cancellation” section and click on “Cancel Account”. This is where it gets a little bit complicated. MySpace will then send you an email with instructions for completing your account cancellation. Except the email doesn’t come right away, and can take a couple of days to show up. Once you get the email, it asks you for confirmation again that you want to delete your account, but then deletes it immediately.
All of the above works just fine, as long as you still have access to the email address you signed up with. But as so often happens when we finally decide to clean up our online accounts, some of them may be associated with outdated email or other accounts. In that case, there are a few alternatives listed by MySpace. The first one is to edit your profile and replace everything in your “About Me” box with “REMOVE PROFILE” and then contact MySpace and tell them to delete your profile (including your friend ID or URL). If that doesn’t work (say, if you can’t login to your account at all), you can just contact MySpace and ask them to delete the profile. How quickly they actually do so isn’t specified.
Official instructions for deleting your account can be found here.