When you link a Revit model to the current model, a message displays if the linked model needs to be upgraded to the current software release.
The message indicates the software release of the model and the release to which it will be upgraded. Depending on the size of the model, the upgrade process can take some time.
If you do not want to upgrade the model that you selected for linking, click Cancel Upgrade. The model is not upgraded, and it is not linked to the current host model.
If you proceed with the upgrade, the changes to the linked model are temporary; they are not saved when you save the host model.
To permanently upgrade the linked model, you must close the host model and then open, upgrade, and save the linked model. The next time that you open the host model, the linked model will not require an upgrade.