Yes. You have to erase it first, then go back through the setup screens to access the backup. If you have anything on it now that isn't in the backup that you want to save, do that first. Then go to Settings>General>Reset, tap Erase All Content and Settings, go back through the setup screens, and when given the option choose Restore to iCloud Backup. You might want to connect it to your external carger first as this may take a while to finish.