I never get subscribed when I reply, I have to do it manually.
Is that what you meant?
....You've confused me now (some might say that confusing me isn't difficult).
A - Under "Profile" > Modify Profile > Notifications and Email, you have the option to tick the box "Turn notification on when you post or reply to a topic". This results in notification automatically after every time you have posted a reply.
B - When replying in Preview there is the "Additional Options" drop down where you can manually each time, or not, select "Notify me of replies".
I'm not talking about either
A or
B but was asking how to unsubscribe threads from the list "
Show new replies to your posts" which is accessed via the upper right in the page header.