How can I change my email address for my iCloud?

See Change your Apple ID https://support.apple.com/en-us/HT202667. 

And see What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071 (supplementary to what the fist link says)

Post back if you have questions about what you can do if your Apple ID (1) is a third-party apple ID or (2) ends in icloud.com, me.com, or mac.com. 

And see iCloud: About your @icloud.com, @me.com, and @mac.com email addresses https://support.apple.com/en-us/HT201771

Note the restrictions in the article.

Apple ID Name Change.        

 What to do after you change your Apple ID or password - Apple Support    I suggest doing this before you change your Apple ID or password.