You can't. If you're going to apply a FLAT paint over Satin, you should sand the wall w/a fine sandpaper first. The new paint will need 'something' to 'grab' on to.
My best to ya and hope this helps.
Jay J -Moderator
PS: Visit your local Sherwin-WIlliams, or whatever, and ask them. Be sure to buy your paint there. (Forget the Home Centers for paint - It's not as good as the paint in the small Retail Stores ...)
PPS: God Bless America!