Having connected your desktop GanttProject to GP Cloud, you can open project files directly from GP Cloud, using the same integrated file management interface which is used for local files and save them updates to the cloud just hitting Save icon or
Ctrl+S on the keyboard. However, there are some additional features and options applicable to cloud documents.
Concurrent update management helps when multiple collaborators work on the same document. It is responsible for sending out update notifications and for preventing unwanted overwrites of the work of colleagues.
More on concurrent updates
Locking management lets one collaborator to lock a document exclusively, so that others just could not update the document while it is locked.
Version history keeps all the recent versions of a document and allows for quick reverting to past versions. So, even if someone bypasses locking and concurrent update detection and overwrites important changes, you can always recover them.
Finally, offline mirrored documents let you work when you have no internet connection and sync back with GanttProject Cloud when you go online again.
More on offline mirrors