A Microsoft Project file can be associated to only one Project Management project. You can remove the association between a Microsoft Project file and a Project Management project at any time.
Note: You should only remove the association if you are sure you no longer need to link the Microsoft Project file to the Project Management project. Removing the link may make it impossible to re-associate the file.
To remove the association:
Open the project in Microsoft Project.
Select PPM > Project Details.
The Project and Portfolio Management Center Integration Details dialog box opens.
Click Remove Association.
If you have already removed the association, the button will be labeled Restore Association, which allows you to restore the association with the same Project Management work plan.
Note: Resource mapping is still retained even though the association has been removed. This allows you to restore the association without remapping resources. Therefore, if you link the project again, automatic resource mapping does not occur (but you can modify the resource mapping manually). See How to Manually Map Resources. If you want to remove the resource mapping from the unlinked file, see How to Remove Resource Mappings from an Unlinked File.