RE: how do I
Not sure what you're talking about.
The posts once people get down replying will fall into the back pages. As long as they're answered, they'll stay on the front lines. The only way to not read them, is to not read them.
There really isn't a way to delete threads that you don't want to read. You just have to work around them.
Does that help? Hope it does, if not, post again.