There are two ways. In regular edit mode on the page (not the category page, you can't remove pages from the category page directly), there is a dropdown menu that will take you to categories. There will be a trash button, click that to remove the category from the page. You can also go into Source mode (also found in the dropdown menu and delete the code itself. It will look like. Erase and save, refresh page, and you'll be good to go!