Within Teamwork, you can rename existing files on your projects.
In the Files area of your project, hover over a file to reveal the additional file options.

Click the arrow button and select Edit File Details from the dropdown menu.

In the file details modal, you can enter a new display name for the file. Below the display name field, you will see the previous name of the file.

Note: The file extension (for example jpg/pdf/docx) will be kept automatically.
For more information, see: Editing File Privacy