Complex sentence: As the song changed from being a ballad to uptempo, Ross became more comfortable with herself and the material; she hummed, sang bit parts, laughed, danced around and even imitated Billie Holiday.
Split into simpler sentences: As the song changed from being a ballad to uptempo, Ross was more comfortable with herself and the material. Ross did was hummed, sang bit parts, laughed, danced around and even imitated Billie Holiday.