All depends how bad it is ,for a quick clean use novus 1 ,if you want to get Most of the scratches out use novus 2 than finish of with novus 1 ,your can use novus 3 then 2 and 1 .
Another way is to take the ramp out of the game and but it in a dishwasher for a bit don't dry it in there as it will knacker it as it is to hot , not done this myself ,but over people do !
There is more ways to clean a ramp but this is the easiest