A 7-year-year-old boy with known moderate persistent asthma attends for annual review. He uses salbutamol inhaler PRN (about 3 times per week) and Beclometasone dipropionate (Clenil Modulite) 100mcg BD via spacer. His asthma control has been suboptimal with occasional night waking and need for salbutamol during exercise. What is the most appropriate next step in his asthma management according to NICE/BTS guidelines?