PR Mapping....Help!

[Ewokinarmor]

Hey guys, I'm trying to erase some textures I placed in my map during my last mapping session, but it won't let me. It'll let me erase one's I place in my current session, though. Is there any way to fix this?
Also, I need to replace some of the detailtextures on one part of my map, but I can't see what I'm doing (even in detail texture mode) because the details don't render unless I'm 2-5 meters away from the texture, and it's really making my eyes bleed. I've seen other screenshots of in-editor stuff where you can see the details from a decent distance away, but I can't figure out how to do that in my editor. Is it just a processor thing?
Thanks.

[Rabbit]

You cant erase after you save, just paint over them.

[AfterDune]

Regarding the detail textures, you sure you set a lowdetailtexture (you set this just once) and clicked "generate"? (or whatever it's called)