Your domain registrar can help you out with this. Because each domain registrar's process is different, we cannot provide you with this information ourselves.
Changing the nameservers is a common process though, and your registrar will definitely be able to change them for you or tell you how to change them. Don't worry, though the process may sound unfamiliar, it's easy!
Your domain registrar is the company that sold you your domain name. If you do not know who your domain registrar is, please check your records for the name of this company and then locate their contact info online.