You should be able to access the account deletion page thru this link.
If that doesn't work for you, use the Contact Us form. One of the available topics there is "I need to delete my user profile".
Note: should you want to delete ALL your profiles, be aware that the account deletion page only deletes your profile on a specific site, so if you have multiple profiles you need to delete each one individually from each site. Depending on how many profiles you have, you may want to use the Contact Us option anyway - but beware that option generally takes a little longer to complete.
Also, as Shadow mentioned, keep in mind that if you are suspended you can't delete the profile (that is probably to avoid user getting out of a suspension by deleting and recreating the profile).