the game wont let me clear tracks and i dont know how to change single player tracks from "X" to "REV"

Hello and welcome!

You can find some of that information under the relevant section in the LFS Manual: http://en.lfsmanual.net/wiki/Autocross

The page don't seem to be updated after the recent patch. So, to select "reverse", when you're in the "X" configuration, simply go the track selection screen (click on "track" just below "garage" and the track map.). Now you can select normal / rev. Although when you're using normal / reverse configuration, you'll have to press "CTRL" to be able to select "X" or "Y".

Once you get used to the track configuration abbreviations, you can directly type in "/track=bl1", "/track=as7Y" to change track [in single player mode or when admin on multi-player mode].