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:
- Change the Viewport back to one you want to “keep”
- Select by ID – use the ID you found above
- 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).
- Rinse and repeat