Is it a steel or aluminum alloy frame ?
The process used will be different for each.
Aluminum frames are anodized - hardened pretty much only on the outside. You want to be careful not to remove that when you refinish.
If steel, stainless or blued ? If it's stainless, it could have a blackened finish. Stainless steel is hard to blue.
You need to know exactly what you have before you can decide on how to refinish it.
It might be better to have it done professionally.