Complex sentence: Henderson was replaced by Jose Melis in 1957, when Jack Paar took over as host from Steve Allen, and in turn replaced Melis in 1962 when Johnny Carson took over from Paar.
Split into simpler sentences: Henderson was replaced by Jose Melis in 1957, when Jack Paar took over as host from Steve Allen. Henderson returned in 1962 when Johnny Carson took over from Paar.