The following tutorial outlines version control feature.
You can check-out an existing file and download it to your hard drive. You can download a file from My Cabinet. Click the icon next to the file name (saying check out) to check out a file. You can have a look at the list of checked-out file in Manage Binder --> File Version Control
You can upload the modified file from your hard drive to AstrixDOC to update a particular file though Check-in option in file version control. Go to Manage Binder --> File Version Control, click on check-in icon to check-in a file. You can add a comment while making a check-in.