Just change your password to something unmemorable and log yourself out.
I shouldnt need to point this out but you might want to delete some on your most recent posts first.
Don't delete the account.
Delete the recent material.
Take a step back.
Ignore any personal stuff posted.
Count to twenty before clicking the post reply button.
No need to delete anything I would think. If you don't want to post on here then just stay off. But you may need it when you get barred from other boards.