Umiya or Ummiyyah means "illiterate", "gentile" (non-Jewish). This is not a bad meaning and there is no reason to change it. The Quran uses this word to describe Prophet Muhammad twice, peace and blessings of Allah upon him.
Say [O Muhammad]: "O mankind! Verily, I am an apostle of God to all of you, [sent by Him] unto whom the dominion over the heavens and the earth belongs! There is no deity save Him; He [alone] grants life and deals death!" Believe, then, in God and His Apostle-the unlettered Prophet who believes in God and His words-and follow him, so that you might find guidance! (Quran 7:158)
Ummiyyah can also mean "one who is like a mother in kindness". Both meanings have the same Arabic spelling of أُميَّة.