how to change my apple ID

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. 

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

You can edit your personal information by logging into your account at: https://appleid.apple.com

Here is a support article with more information: https://support.apple.com/en-us/HT202667