how to change from old apple id to the new apple id
How to change my current Apple ID to the new Apple ID ? What is the step?
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)
And FYI, see iCloud: About your @icloud.com, @me.com, and @mac.com email addresses https://support.apple.com/en-us/HT201771
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.