Hi Miranda...
After you have removed the paint, as described karin, you can do the following......
-then clean the helmet good with a silicone degreaser.
-next, grind the helmet with water sand paper P800-P1000.
-next step...use a good primer for plastic and then a sanding primer.
-this grind again with P1000 water sand paper.
-clean the bucket again with silicone degreaser.
-then paint the lid again in the desired shade.
I hope this helps
Greetings,
Dan