Will the 11-year-old “I’m Lovin’ It” jingle—an earworm if ever there was one—soon be just a memory? After all, McDonald’s recently hired ad agency Leo Burnett to refresh its image.

The Oak Brook, Ill.-based McDonald's Corp. revealed Friday a series of ads that reaffirmed the operator’s decade-old “I’m Lovin’ It” campaign with an upbeat message amid one of the ...