How to change a facebook setting?

[rene]

I can't find the answer to your question from the FB settings.
However, you can do it manually. That is, every time you comment or post something on your friend's wall, you'll have to go and delete the story on your wall.
On your wall/profile, move your cursor to the upper right corner of the "story" (I'm not sure if that's what they are called) until the x appears. Then click the x to delete that story.