I'd like to re-start. How do I delete all the previous work?
It is possible to delete an App in Salesforce but the App (as defined by Salesforce) is really only a shell that points to the other objects that make up the functionality you defined in your project plan.
1) Goto Setup
2) Search for "App" in the search box on the left sidebar
3) Click on "Apps" under Create
4) You should see a list of existing Apps.
5) The "Festival App" is a custom app and should have the "Del" to the left of the App name.
6) Click on "Del" to remove the app.
However, if you want to completely "start over" you'll need to delete Reports, Dashboards, Workflow Rules, Objects, Tabs, Master-Detail Relationships, Rollup Summaries, and a few other things I probably forgot.
These items all need to be deleted individually before you can consider the entire "App" to be deleted.