You can edit Categories and Forums using [pencil] icon-button located on right side of each forum panel in Dashboard > Forums > Forums admin page.
Click on this button and do the changes you need using “add/edit forum screen” options.
Don’t use this button if you just need to change forum parent or order. You can do that on this page by dragging and dropping forum panels. Then save changes using [Save forums order and hierarchy] button located on the bottom of this page.