how to ?

Acetone & Thinner breaks down paint.. Try it on a rag and wipe.

Thing is.. how do those plasctics look under all that paint.
Might have to redo the prep work & re-paint.
 
Carb cleaner takes paint right off plastics. But like climb said the plastics might be too nasty to ever look right, your best bet would be to sand it down and use a good industral paint and clear coat. Or better yet if you have a sprayer use autobody paint.
 
Brake fluid on a rag... Then sand till you have uniform scratch marks, at like 1200. Then use a wool buffing pad at 1500 rpms w/ 3m buffing compound on a rotary buffer, then go to lighter pads, until you get to final polishing stages.... It's an ass ton of work, like said previously just get the paint off and sand and clear.... or get new plastics. Too many cheap sets of plastic out there...
 
i took paint stipper to mine. just do light coats and be careful not to melt the plastic. it took me like three coats to get mine off and i rinsed them with soap and water between coats. its easy and quick and it only cost me like 12 dollars at ace for the strippper