I want to change my Apple ID

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

And, here is 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. 

Change your Apple ID - Apple Support