Complex sentence: Guitarist John Sykes was hired to replace Snowy White after 1981's "Renegade", and Sykes helped to provide a heavier sound and guitar tone than Thin Lizzy had used on previous albums.
Split into simpler sentences: Guitarist John Sykes was hired to replace Snowy White after 1981's "Renegade". Sykes provided a heavier sound and guitar tone than Thin Lizzy had utilized on previous albums.