Where to renew your CNA depends on what state you are in. Most require you to take a test if you have not been an active CNA for three years or more. If you have all you do is present your credits to the certification office and they will issue you a renewal. If you have been out of it for 3 or more years you need to contact whomever your state uses as a certification agency and retake the test.
. You can take a course or just take the test cold. There are several online agencies that provide review or refresher courses. Usually the state that you live in will have all of this information posted on their website.