Within Teamwork Projects, any file that has been attached to a task can also be removed at a later date.

To detach a file from a task, navigate to the Tasks area of your project.

Locate the task which has the file attached and select it. You will then see an option to Manage Task Attachments.
When you select this, you will see a checkbox option next to each file that have been attached. To remove a file, uncheck the box next to the file and select Save Changes.

For more information, see: Adding a file to a task