Hi, the simple answer is not to do it. Upvc is not really made to be painted and the chances of it staying on without some of it peeling are slim. Dulux do make a upvc paint but I think it only comes in white, just in case you wanted a different colour. There is a product called ESP which is used to prime plastic which you could use to get it ready for painting if you decide that you want to go ahead with it. Just follow the instructions and hope for the best. Good luck.