A 62-year-old woman presents with a 2-week history of increasing breathlessness, cough, and wheeze. She has a past medical history of asthma, for which she uses a salbutamol inhaler as needed and a low-dose inhaled corticosteroid (ICS). She reports using her salbutamol inhaler 6-8 times a day for the past week. Her current PEFR is 60% of her personal best. What is the most appropriate next step in her asthma management according to BTS/SIGN guidelines?