You ask the parent or employer who paid for it and had it installed to remove it.
WebWatcher is not an app I endorse, or approve of in any way (not that that matters) but it's not Malware and doesn't randomly install itself. If you believe it was installed by someone or something that shouldn't have access to your phone, contact WebWatcher WebWatcher: Computer & Mobile Monitoring Software and ask them to investigate who the app is registered to and who has access to the online account.