Within Teamwork, you can move files between different categories on your project.
Go to the Files area of your project and hover over the relevant file to reveal the additional file options.

Click the arrow button to the right of the file and select Edit File Details from the dropdown menu.

Note: The option to edit file details is not available when a file is locked for editing.
At the bottom of the Edit File Details modal, you can choose a new category from the Category dropdown. You also have an option to create a new category.

Drag and drop
You can change a project's category by dragging it to a different category in the Categories pane on the left in the Files area.
Hover over a file to reveal the move icon (vertical dots) to the left of the file name. Click and drag the file to the new category.

You can also select multiple files to move to another category. Click the options button (three dots) in the top right of the Files area and choose Select Multiple Files from the dropdown. Alternatively, press m on your keyboard.

Using the checkboxes, select the files you want to move, then drag them to the new category. You can also use the orange Move or Copy button at the top of the files list to select a new category.

For more information, see: Managing Multiple Files