You're right, that BPM thing doesn't work. There is one other thing you can try. At the bottom of the screen below the waveforms of the songs you are mixing, look for red boxes with numbers in them. These boxes are connected with red lines throughout the whole mix. If you click on the box, below the song that you want to adjust, and hold down the mouse button, you can drag the box higher or lower to raise or lower the tempo of the song. Hope that helps.