You can try a few different things.
1) wash them down with TSP(tri-sodium phosphate). Make sure you rinse really well.

2) lightly scuff them up with either a peice of sandpaper or sanding block, so that the new paint will adhere better.

Also, it doesn’t hurt to call your local hardware store and consult a professional paint expert for a second opinion. It’s always good to have a contingency plan.

Hope this helps:)

Work like you don’t need the money, Love like you’ve never been hurt, and Dance like no one is watching……