From the Landing page, navigate to the file/project from which you'd like to remove collaborators from, then:
Select the file: single-click on it
Notice the collaborators listed beneath INFO on the right of the page:
3. Hover your mouse over the collaborator you'd like to remove
4. Notice the X delete button appear next to the collaborator's name
5. Remove the collaborator: click on the X delete button
Removing collaborators from projects will not delete their analysis - their replies and event tags will remain visible and accessible to you and other collaborators.
Removed collaborators can be re-added to projects again later.