change icloud

If you want to change the primary email address on the account (and if it's not an Apple domain address) log out of it everywhere and change it : Change your Apple ID - Apple Support

To change the account's password : Change your Apple ID password - Apple Support

Your iCloud ID is an Apple ID. Do you have 2 Apple IDs? If you log in below using your Apple ID, does the iCloud email address show there? If it does, you have 1 Apple ID. To change the password of the iCloud email, you have to change your Apple ID password. You can't remove/change @iCloud.com, @me.com or @mac.com aliases.

Apple ID - Manage

If your iCloud email doesn't show at the link above, you have 2 Apple IDs. You can then use the links above to change the 2nd ID.