Can I remove files in previous courses, ie previous cohort?
Hi Arthur Leung and Welcome to the Canvas Community! This depends on the settings that your Canvas Admin has set up on your instance. If your courses are not closing (by date or conclude) then yes, you should be able to continue to edit the course (delete files) and build the course as you see fit. If you are talking about deleting student content, you should have the option to simply reset the course and start new (I would recommend copying the course over to a development course shell to save what you have done before you reset it.)
Retrieving data ...