When necessary, new versions can easily be uploaded to replace older versions. Users will still have access to older versions of the document, including notes and messages.
To do this
Click the cogwheel to the right of the document and select Add new version. To view other uploaded versions, click the cogwheel and select Document Properties. This is the revision summary. The most recently uploaded document will also be marked Current.
In the app: When you are in the document, sweep to the left to bring up the document history (Requires that you have the most recent app version installed).