That's "losing" them.
First, title all your tracks (see the manual for details on how to do that). Select the track you want to move first, then press the TRACK button. Scroll down to an empty virtual track (like TRACK009 or something) and press ENTER. This will remove your titled track and replace it with an empty virtual one. Then Select 7/8 and press TRACK again. Scroll down to your titled track and press enter. This will move it to channel 7. Repeat for track eight, but notice the little tabs at the top of the screen after you press the TRACK button - use the left/right cursor keys to move from one to the other. That's how you get to track eight.
If you want to bounce tracks 1-6 to 7/8, press the QUICK SETUP key and look for 'bounce to 7/8'. It will route all the tracks for you automatically. But you'll still have to arm 7/8 and play the tracks to bounce.
As always, the manual is your friend.
