Q: iCloud

went to settings and followed instructions to change iCloud info...here's what i'm still dealing with...on my iPhone 5s, 8.1.2, when i go to settings to the iCloud icon, right below it still lists my old Yahoo address...this is causing conflicts on my iPhone and iMac...i need to delete that address and change it to a different address...how do i do that?...i have an updated Apple I.D. and password, what else do i need to do?