best way to increase project tempo

Working with a copy of the project so you have an unstretched backup:
 
- Select all audio tracks.
- Hit A to bring up the Audiosnap palette.
- Verify the dropdown to the right of Clip Follows Project is set to Autostretch
- Click the Clip Follows Project button.
- All clips will now show a transient icon in the upper right corner, and will follow any changes you make to the project tempo. 
- Don't go too crazy or you'll get bad stretching artifacts, although increasing tempo is usualy less damaging than reducing tempo.
- Once you got the tempo(s) you like, you will want to set appropriate Offline stretching algorithms for each clip individually in the Options section of the Audiosnap palette, and Bounce to Clips to render the stretching permanent