Nassar,
Here is a Zip-Dee link that will give you a 1, 2, 3 instructions on replacement.
http://awningsbyzipdee.com/2815/index.html
Polishing is possible. If your expectation is to take a matte finish and make it chrome shiny, I'm not sure you will accomplish that without some extreme polishing that will require more than just some metal polish and elbow grease. If you're looking for the chrome shiny it is possible to purchase the highly polished arms & metal casings from Zip-Dee.
Hope this helps........................