You should talk to your doctor or whoever first, cold turkey is almost never the best way to get off of any drug.
crazymeds doesn't have anything to say about getting off of risperidone
http://www.crazymeds.org/risperdal.html However, there is a lot to say about Prozac,
http://www.crazymeds.org/prozac.html,
Unlike other medications, the time to step down from Prozac isn't based on half-life, it's based on anecdotal evidence. In other words, people's experiences. Now, if you start to experience SSRI discontinuation syndrome once you're down around 30-40mg a day, then you will have to look at reducing your dosage by 10mg a day every month.
However, that is from a higher dose, so coming down from 40 mg would probably be quite a bit easier.
Overall though, tapering off the meds is better by far, talk to your doctor.