Just use the same stuff you use on your paint,.. because they are actually clear-coated...
... but,.. if the discoloration is under the clearcoat, the only way to remove it is to remove the clearcoat...
Then,.. you'll either have to keep it polished or re apply a protective coating...

I dont like chemicals, so, I went at it manually. After some laborious & very slow approaches, I found a green Scotch Brite pad will mount like sandpaper in a palm sized orbital. A spray bottle of water & a sprits on the case & a few on the pad. If you run it too long, or run it dry it will make the aluminum very dark,,