exit windows insider

Press Win + I to go to Windows Update, find the Windows Insider Program and tap Stop Getting Previews. If you want to roll back to the Stable version (note that you have to do this within 10 days), go to Settings > System > Recovery, select Back and follow the wizard's instructions.
Note that rolling back will keep the files but uninstall recent updates, and install the stable version if it's been more than 10 days.