Click the Compare button in Object and Instance Data and select the model that contains the new data.
You are then asked "Use RealTag for Matching?" Answer No if the model has not changed structured (eg Object Deleted and then Reinserted, or a level removed) - and the compare will be done using the InstanceID
If you answer Yes the compare is done using the RealTag. This provides a way to import data from a model that has been restructured but still produces the same RealTags
The Instances table will then be updated to show the changes data, with the current value in  underneath.
After comparing clicking the Import button shows a list of the changed fields with which you can select which fields to import the data from.
Imports are recorded in the model history