If the account is deleted, he/she will not be able to access the site except as a guest
The easiest way of deleting an account is to treat the member as a spammer, delete all threads and ban the user. However that also deletes all responses by other members.
It takes longer but it is possible to delete all the user's posts leaving the other posts intact...but this can make the remainder of the thread somewhat incomprehensible. I know this from personal experience at UA. Imagine this thread without post #1...
Or all the threads can just be locked
I've asked the OP to review his/her decision based on another recent poster (latter banned) who asked for his account to be deleted then changed his mind when I checked!
Personally I wonder why the OP doesn't just stop posting / visiting the site