hi, a lot depend on how bad they are!! if there not too bad then you can use a fine cutting compound like `T cut`Farecla G10, Festool 5,000 speedcut, with a felt attached to a drill (must be variable speed) use the drill at a very low speed so you don't build up any heat (make sure you use enough compound, and add some fine spray of water if it starts to dry out) and this should work out fine. ideally use a small 90mm polisher at speed 2-3, but most do not have access to these. If the scratches are bad, then you may have to use very fine abrasives first, 1,000g, 1,200g, 1500g. do some tests first on some plastic (acrylic glass) to get used to the speeds that would be ideal and feel the glass every so often to see how hot it gets (can get warm, but not hot), Hope this helps