Complex sentence: In 2011, Mauriello announced she would be leaving Lazytown due to her age and was too big to play Stephanie and was replaced by Chloe Lang for season 3 and 4.
Split into simpler sentences: In 2011, Mauriello announced she would be leaving "Lazytown", having grown too big to play the role of Stephanie. She was replaced by Chloe Lang for season 3 and 4.