If you changed a model which is used in another model, then there is still the old version used. You might want to update the used model to its latest version. There are two different ways to do that. You can either do it from the referenced model or from the model who uses the other model. Let's do this with an example this will be much easier to understand. So you have a process map and in that process map, you linked a process. The process is the referenced model and the process map is the model who uses the process model. Now you modify the process model and therefore get a new version. But in the process map, you still use the old version of the process.
From the process, you can manage the used version in the Main tab under the section Model Management with the button Usages Overview.
With a click on the Update Usages button in the left bottom corner of the dialog, you update all versions to the latest one.
Or you can also do this over the process map. There you have to click the button Manage Used Models in the Main tab.
In the opened dialog you see all the models the process map uses. Now you can manage the version for every single used model. Either you choose the version directly at the listed model or you click the Update (Latest Version) button.
The second way has the disadvantage that the version of the process model is only updated in the process map. All other models who might use the process model still have the old version in use.