There is not a way within RM. Outside of RM, it can be done with an SQLite script.
Normally, changing one fact type to another would be an extremely simply script within SQLite, assuming you were up to installing SQLite and running a script. For the Alternate Name fact, the script would be slightly trickier than usual. It would not be rocket science, but it would be slightly tricky. That's because all normal fact types except for one are stored in RM's Event Table. The exception is RM's Alternate Name fact which is stored in RM's Name Table. So for your particular problem, each of your Alternate Name facts in the Event Table would have to be converted to entries in the Name Table, and then all your Alternate Name facts would have to be removed from the Event Table.