A 32-year-old man with schizophrenia has been on risperidone 6 mg daily for 8 months. He presents to the psychiatry clinic with complaints of progressive difficulty in maintaining erections and decreased libido for the past 3 months. On examination, he appears well-groomed and cooperative. Laboratory investigations reveal serum prolactin 85 ng/mL (normal <25 ng/mL). Testosterone is 250 ng/dL (normal 300–1000 ng/dL). What is the most appropriate next step in management?