Family Historian User Group

My Mother was born illegitimate, her birth mother went on to marry another male a few years later. The problem I have Family Historian shows the later married male to be my mother's father, which is not the case. How do you alter relationships on Family Historian to so this fact?

You need to create two family partnerships, similar to multiple-marriages or foster/adoptive parents, and then link the children to the appropriate parents. See the following that show the techniques to use although in slightly different contexts:
how_to:recording_children_other|> Recording Children for multiple partnerships
how_to:recording_children_with_foster_adoptive_parents|> Recording Children with Foster/Adoptive Parents
how_to:changing_relations|> Changing Relations
how_to:removing_unwanted_relations|> Removing Unwanted Relations

If you still cannot figure it out then ask again.