Aslakson changed to Nasset

I find six Nasset children born to Ole Aslakson b. 1823, Vinje, Norway, and Anna Hagerstrom, all in the late 1800s. Swemong, Aslak, Asbjorn, Andrew, Helga, and Annie. Does anyone have an answer as to the total transformation of the last name? The excellent article on the web site does not address this. Thanks very much.