Old data remains in drop box after switching data type

Old data remains in drop box after switching data type

I had a drop box that has several choices in it, I then switched the field to an import field so that the choices were loaded from another form.  When I access the application the new choices get imported as choices but so do all of the old static choices that were originally put in the drop box.  How do I remove this old choices and only load the data from the form via the Lookup field?

Thanks,
Dustin