ICloud Assistance

Hi!

My original icloud account was created with ****@nc.rr.com. I have since changed it to my active email which is ****@gmail.com. However, my Icloud on my Macbook Pro is still under the old email , ****@nc.rr.com. How do I sign into my gmail Icloud information? My messages on my computer are not working and I think this is because my computer is still under my old Icloud email account. Thanks for your help!

[Email Edited by Moderator]