Complex sentence: Sierra announced his retirement in December 2008 and accepted the position of manager with his beloved Unión Española, he will continue on the position until the end of the Clausura 2009 tournament.
Split into simpler sentences: Sierra announced his retirement in December 2008 and accepted the position of manager with his beloved Unión Española. He will continue on the position until the end of the Clausura 2009 tournament.