Hi Kim, it looks like you might have recently merged yourself with your father's profile, instead of adding him as your father? (Profiles should only be merged if they are duplicates that represent the same person.) You might want to contact the info at WikiTree email for help getting your account/profile sorted out.
Changes to relationships in the global tree are made by clicking the "Edit" tab in the profile page, and clicking one of the "Edit Family" links on the right-hand side. (See: Help:How to Edit a Profile). So to remove your father's father click "Edit" on your father's profile page then click the "replace/remove father" link and select remove. Then you can create a new profile for his actual father by going to Edit > Add Father from his profile page.