A 52-year-old man with a 10-year history of hypertension presents to the outpatient clinic. He has been on amlodipine 5 mg daily for the past 3 years with reasonable blood pressure control (BP 138/88 mmHg). However, over the last 2 months, he has developed persistent bilateral ankle swelling and gum hyperplasia. His renal function and electrolytes are normal. He denies any new medications or dietary changes. What is the most appropriate next step in his management?