The BPMN Modeler allows you to keep track of all your previously created diagram versions. Via the “more“ submenu → Version Control you can open an overview of all the versions created for the current diagram.
From this dialog you may:

• set milestone versions. You can mark special versions by clicking on the star icon and giving them a name so that you can easily identify them later on.

• reopen an older version by clicking on the version number. You can now edit this version in the modeler. When you save your changes, a new version will be created and saved as the latest revison of your diagram.

• see information about the author and the publication date.

• see descriptions attached to diagram versions (see diagram settings for more details).

• view differences between two diagram versions by comparing diagram versions.

Aside from allowing you to manage and review diagram versions, you can also compare them and see all changes depicted visually in the diagram as well as listed in a table.
To do this go to the “more“ submenu → Version Control. You may select two diagram versions you want to compare by clicking their respective checkboxes in the leftmost column. After clicking the compare button at the bottom of the version list, you have the two versions displayed side-by-side.

Changes are colored according to whether something was added, deleted, moved or changed. You can click on the entry in the list of changes and the changed process element will be highlighted in the two diagrams. If an element has changed attributes, e.g. name or description, it will be displayed with an attribute box, showing the old and new values of attributes. These boxes can be toggled by clicking on the element directly, or you can toggle them all at once by clicking on the “Changed” Symbol in the top right corner.