If you only need the occasional Umlaut, using the ASCII codes is the easiest way, as the previous poster said. Just make sure that the Num Lock light is on, and that you use the numerical keypad to the right of the keyboard. Alt plus 129 gives you ü, for example, as in Grün. If your ancestor lived in England, he must have had problems with officials rendering his name correctly in documents. I'm surprised he wasn't tempted to anglicise it to Green, which is what "grün" means. He may have sometimes used the version Gruen, to compensate for the English bureaucrats' inability to cope with the Umlaut.