Actually both are correct although Abraham is the more important of the two because it is a "covenant" name. He bore the name Abram until he was 99 years old when it was changed to Abraham.
Genesis 17:1-5 [RSV] 1 When Abram was ninety-nine years old the LORD appeared to Abram, and said to him, "I am God Almighty; walk before me, and be blameless. 2 And I will make my covenant between me and you, and will multiply you exceedingly." 3 Then Abram fell on his face; and God said to him, 4 "Behold, my covenant is with you, and you shall be the father of a multitude of nations. 5 No longer shall your name be Abram, but your name shall be Abraham; for I have made you the father of a multitude of nations.
I hope you have found this helpful.