1. Go to the website you're having difficulty with (E.g Exam.net)
2. Click the Site Information button located in the address bar
3. Click on the Cookies and Site data option
4. Click Manage on-device site data
5. Click the little trash icon next to any of the sites data is being stored from then click Done
6. You'll then be asked to reload the page by clicking the Reload button that has now appeared