Organization administrators can set the frequency at which a new version of a file is backed up, how many different versions of a file are kept, and how long old versions and deleted files are retained. Here are the default settings:
Administrators can change these settings for their organizations using the web console. While viewing your organization details, choose Device Defaults... from the gear menu. On the General tab, uncheck Use device defaults from parent.
Then change frequency and version settings on the Backup tab.