A 78-year-old woman with non-valvular atrial fibrillation presents for stroke prevention review. She has hypertension and prior transient ischaemic attack but no history of bleeding. CHADS-65 criteria are met (age ≥65 and prior TIA). She is currently on aspirin 81 mg daily. Renal function is normal. What is the most appropriate change to her antithrombotic regimen?