There isn't really a process for it and certainly deleting posts is not something any forum usually does when a user leaves (as it leaves every thread they participated in full of gaps). If you are determined to burn your bridges, you can:
1) Remove avatar, signature and all other personal information from your profile.
2) Empty your private messages then turn the feature off.
3) Change your email address in your profile to something non-existent.
4) Change your password using a strong password generator to create some random PW you haven't got a chance in hell of remembering and copy/paste it. If your browser asks you if you want to store it, decline.
5) Log out and clear any cookies for good measure.
You have now rendered your account unusable.
Before you take the dip, however, bear in mind that closing down an account and resurfacing under another user can be frowned upon in the absence of any reasonable justification for the identity switch. Multiple accounts for the same individual are generally not welcome.
