There's no easy way to delete a single app from your 8x8x8 Cube, but you can reset to the original demo reel if you have a PC with Cube Doctor. The process is still a little buggy, so any feedback is much appreciated.
First unzip the files below into a folder and then just connect your cube via USB cable to your PC, launch the program and click "Fix my Cube".
*MAC Version (we're fixing a bug here, hope to have this version back up and running soon)
Let me know how it works for you to bring your Cube back to the most up-to-date factory condition, and then please try the Photon connection process again via the Particle App.
-Shawn, Looking Glass