How to Delete Viewport Title Types in Revit

Firstly, consolidate your Viewport Types by using Select All Instances - In Current Project and switching them to the Types you want to keep.

Then, change a Viewport to one you want to delete, and use Snoop Current Selection (RevitLookup).  You can drill down to find the ElementID of the Viewport Type Definition:

Ok, with this in hand:

1. Change the Viewport back to one you want to "keep"
2. Select by ID - use the ID you found above
3. Press Delete on the keyboard (if any viewports still use this definition, Revit will prompt you that deleting this Viewport Type could cause problems etc). 
4. Rinse and repeat