A 38-year-old man with schizophrenia has been on risperidone 6 mg/day for 8 months. He presents with involuntary orofacial movements, tongue protrusion, and lip smacking that began 2 weeks ago. Vital signs are normal, temperature is 37.2°C, and creatine kinase is 180 U/L. What is the most appropriate next step in management?