As far as I'm aware there is no way to purge all of the progress from your account and start over.
Realistically with the amount of time and effort which needs to be invested in unlocking the various characters and accumulating the various customization items I simply can't think of a good reason why anyone would want to completely restart; the only portion of the game that can't be revisited as often as you want at any time is the very first scene where you, as a Plant, spawn in Zomburbia and have to fight your way out as the game goes through its basic tutorial.
Thanks for your reply. The reason I wanted to start over at the tutorial level was really for my child to experience it. I was just testing out the game before letting him play it. I wanted to make sure I understood how to play it and show him how to play. I know if I was the programmer of the game I would be highly upset that people only get to experience and see that tutorial level for only 5 minutes or less before being picked up and taken to the next level and never getting to see it again.
