How to get windows clear again

I accidentely painted over my windows while I was re-texturizing an outside wall. How do I get it back to look like a window? Also if I wanted to change out windows-rectangular for oval; I guess that would be a huge building project, because of walls & difference in opening? Was trying to make a regular wood house stucco/spanish. Also is there a way to copy a texture if say I have wood texture tha came on house & I want to go back to that texture. How do I know where to find or is there a way to copy that to use on rest of house?
Thanks in advance for all your help!

You might want to try the Building Tips forum:

/8/1.html

Also, you might want to say if you're building the house from scratch or modifying a prefab. And, if it's a prefab what are your permissions.