The only way is to go back and delete your reply or replies in that thread. I wish it were simpler than that, but this is something that bugs the crap out of me, as well.
That would be a lot tedious and difficult task if you made many different posts and at time intervals.
You have to disable the notification in a specific thread or board by clicking the notify button. A pop up message will appear to disable or enable the notification if theres a new reply of that specific thread.
I think the "Notify" option is used to send notifications via e-mail, so disabling that is not going to help i guess.
A better approach is to start using "Watchlist" instead of "Updated Topics". You can easily watch or unwatch a thread without need to delete posts and affecting your post count.
