How to clean lenses

I have few "white" lenses what starting to turn yellow.
Does any one know cure for this? Does anyone know how to clean aluminum lens to make it shine again? How to get read of scratches on the metall? And what to do about fungus? How to get read or it?
(lenses are Mir-1 and Jupiter 11, 39mm screw mount)

To clean off yellow you can try Brasso metal polisher, but you need to be VERY careful not to get any on the glass...

Where can buy it?

Well this particular one is sold in USA, but probably any universal metal polisher will do if you cannot find this one. Where are you located?

Vlad.