Dr. Miller believed the family had been in England for many years, though may have originated elsewhere (with a particularly interesting possibility of Huguenaut origins). As for the so-called "name change," I wouldn't put too much credence in that. Often in these 17th or 18th century records, there may be only a single record or a handful referring to a particular individual, and spelling was not standardized in those days. Just have a look at the way census takers in the 19th century can butcher just about any name, spelling it as "sounds like." Just because an early record says "Dymett" and later records say "Dimmitt," that doesn't suggest that somebody deliberately "changed" it for any particular reason.