Step::1 Login to RedServerHost Client area.
Step::2 Navigate to Domains section and click on My Domains.
Step::3 Now click on the Active button near your domain.
Step::4 In the Overview section of the screen click on Nameservers.
Step::5 Enter the Nameservers and then Change Nameservers.
That's It !
Check out the video tutorial explaining the above mentioned proceedure in detail. You may refer to the blog as well.