The maximum upload file size on the Bilkent Moodle is 2 gigabytes (2048 MB).
To reduce the size of a your course’s backup archive file (.zip or .mbz), try and switch to hosting very large files, such as videos or high-quality color pdfs or images, on an external cloud service (e.g., youtube, google drive, box, etc.). Embed code or links pointing to the files will take up much less space in your Moodle course.
Make these changes before you back up the course to see a reduction in the filesize.