Lund/Johansen in Skiptvet

I am new to this oversea's research and do not quite understand how to find things. The problem seems to be when they came to the US they had the Johansen name. they came from the domicile Lund. so they changed the name to Lund here. Nobody alive now knew of the Johansen name until yesterday! How do i figure out how to go further back? All I have is the 1900 census in Skiptvet that gives the parents names. which is a start, but how do i go back any further? Seems they change the names around alot! Jens Marius Johansen dob 19 Jan. 1895 (my great grandfather) father Johan Johansen mother Johanne JOhansdatter siblings: Edvin, Hans, Hilmar, Marie, and Asta lived in skiptvet 1900