First thing to do is open the session and choose "Save As" and give it a new name(like "song at 172bpm"). This way, no matter how bad you mess it up, you can open the earlier version
Next, put all your audio tracks in Ticks mode(usually they default to Samples mode, but there is an option under the preferences menus). Then, enable Polyphonic Elastic Audio on all audio tracks. Now change the bpm. With a little luck, the song will play at the new speed, and if you don't try to go too far, it SHOULD still sound good.
Now the above all happens in PT, but there are other options available. One is Serato Pitch 'n Time, which works as AudioSuite. So you could take your 2-track mix(after Bounce to Disk), import it into a new blank session and highlight the entire track, and let PnT change the tempo(they have a free 14 day demo). I also use Wavelab and it has a time compression process that does much the same(taking a 3 minute song and make it fit in a 2:45 time frame makes it faster, without changing the pitch). Hope something here works
