If you don't want to overwrite your original diagram after making changes, you may work with versions of that diagram.
Save New Version
The following dialog will be displayed. You can now enter a name for the new version and a description.
Open an older version
If you want to load a previous version of a diagram, click on "Open" in the quick access toolbar or the application menu. In the file selection dialog you may now navigate to the diagram. After selecting the diagram, click on the arrow of the splitted OK-Button and then on "Show Previous Versions".
You may then choose from a list of available file versions of the selected object. In addition you'll find a Properties entry in the application menu. The properties dialog contains a "Versions" tab which provides the required information.
Load a diagram version via URL
Generally, you may load a diagram via URL. To get the URL, open its file properties, e.g. as described above or by right-clicking on the diagram in the process explorer.
Copy the URL to the clipboard. It should be something like this:
The URL will load the newest version of a diagram. If you want to load a specific version, add the URL parameter "version" or short "v" to the URL. In this parameter, the version number is passed. The result should look like this: