Question

How do I change a surname?

Answer 1

See this: https://www.wikitree.com/wiki/Help:Correcting_a_Last_Name_at_Birth

And, make sure you have ample primary source documentation for making changes to any Last Name at Birth.

Answer 2

If the Last Name at Birth (LNAB) is correct, but they later changed their name (got married, etc.), then you change their surname by putting it in the Current Last Name field.