Relatives who changed their name can create research challenges. Your ancestor might have changed their name without going through the legal process of making an “official” name change. There are some ways to document the change.
Military service or pension records may document name changes. Land records may document a name change if the seller was using a different name than when he acquired the property. Probate records may refer to a previously used name by the deceased individual. A divorce record may mention previous names used by one of the parties. Criminal court records may also reference aliases or other names used by the defendant. If you are biologically related to the person who changed their name, your DNA matches may help you determine their true identity.
The problem with name changes is connecting the person to their earlier name. Some records make that connection easier than others.