Within Teamwork Projects you can edit an existing category name if you wish.
Categories can be found within Messages, Files, Notebooks, Links and the Projects lists view.
To edit a category in one of these areas, hover over the category header in the left pane and you will the option for manage to appear:
When you select 'Manage' you will be presented with your list of created categories:
You can then select the category you wish to rename and edit the existing name.
You also have an option to assign the category color and move it to an alternative category.
For more information see: Changing a project category