Board Thread:Support Requests - Getting Started/@comment-35701214-20180527061829/@comment-1038387-20180527084957

Go to the page you want to delete. In source mode, there's a module on the right side of the screen. If it's not there, there should be a tiny < in the middle of the edit window. Click it, and you see the module. You can hover over the category and a trashcan appears.

If you want an easier experience, go to MyPreferences > Editing > Turn off Category Module. Now, the categories will appear as plain wikitext in source mode.