How to paint wheel rim?

Thanks for asking this question. This is actually not a painted wheel I would not recommend trying to sand it and paint it. In fact you are going to have to get a repair kit that is made for alloy wheels. You can do an internet search as there are a ton of products. Just search "repair damaged wheels" and look for alloy wheel specific solutions as there are other types of wheels.

More then likely you would need to take the clear coat off with a sand blaster (not sandpaper) and then polish the metal and then clear coat them again. So unless you are want to go to that extent, you are going to be stuck with just trying to improve the appearance with one of these kits.

Unfortunately this is pretty common so the kits do a pretty good job but again, sanding them down is probably not the best idea.

Take a look at some of these kits and let us know what questions you have. Thanks

Thanks.
But actually my purpose is not only to repair the scuff , but i want to change the color from metallic gray to matt black. what are the steps to do so?
Thanks

Okay. That changes things. I would not try to sand these. There are so many tight spots that you will not get to so I would suggest sand blasting them. This will take them down to bare metal and then give a clean surface to paint.

Just make sure you are using a high quality paint specific for wheels. There are a lot of brands out there but just go with a well known name brand.

So if you sand blast them that will ensure all the areas are scuffed and all debris and contamination is removed so that the paint will stick to the wheel and not any dirt or grease that will cause it peel.

Let us know how they turn out.