A 65-year-old woman with NYHA Class II heart failure (EF 35%) is on ramipril 5 mg daily, bisoprolol 2.5 mg daily, and spironolactone 25 mg daily. She reports persistent dyspnoea on exertion and ankle oedema. Her BP is 105/68 mmHg, HR 72/min, K^+^ 4.2 mEq/L, and eGFR 52 mL/min/1.73m². What is the most appropriate next step in management?