Navigate to the company that you want to work on. Once in the company click on manage lists on the left of the screen.
Then choose the Tax Code tab or Categories tab at the top of the page.
Category codes and names (or Tax Codes/% Rate/Descriptions) can be edited and are automatically saved.
You can delete individual codes by clicking the trash can to the right of that code. Multiple codes can be deleted by checking the checkbox to the left of the desired codes and clicking Delete at the top of the page.