How Do I Change the Class of a Model? (Magic xpa 2.x)
Once a model is created, you cannot change the class of that model. After you fill in the initial values for the model, the class becomes locked as soon as you move the cursor off the model line onto another model. If this happens on a newly-created model that has the wrong class for some reason, just use F3 (Edit->Delete) to delete the model and start over.
However, if you are not sure if the model is being referenced or not, you can check this by pressing Ctrl+F (Edit->Find and Replace->Find Reference), before deleting it.
Using the Cross-Reference