i did it with a pair of cheap pair of black jeans cause i didn't want to sacrifice my Levi's but its the same steps, put them on first, take a silver sharpie or something that would show up on the fabric and make a little mark just below your knee to account for any shrinkage or fraying when their cut, take them off and use a ruler to draw a straight line then carefully cut along the line to make sure it stays straight, repeat with the other leg, then use a lighter to singe the ends of the fabric or use some fray check to stop it fraying like crazy