1- Factory reset
From the "Troubleshooting" page (wrench icon on the top right corner of the dashboard), click on "Factory reset" to bring back Xangle to the default settings (this also removes all of your files)
As an additional note, these files are stored in c:\users\your-user-name\xangle. Before proceeding, you can backup this whole folder (duplicate it). You can always revert by bringing back your manually created backup files
2- Granular reset
From the same page, scroll down to reach the granular reset items. This is a great way to clear a few items without removing everything.