Complex sentence: Ownership changed again in 1976, and it became the Radisson-Cadillac until 1979, when the Radisson chain sold it, it became the the Book-Cadillac once again.
Split into simpler sentences: Ownership changed again in 1976, and it became the Radisson-Cadillac. In 1979 the Radisson chain sold it, and it became the Book-Cadillac once again.