I want to change my Apple ID mail name

You can change your Apple ID email address on your current Apple ID so you retain access to your data and prior purchases. Note the restrictions in the article.

Apple ID Name Change.  * 

Make sure you turn off Find My Phone before signing out of the old ID. Once signed out and Find My Phone is off, then sign in with the new ID, then turn Find My Phone back on.

 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.

Apple ID -Two-factor authentication   *

You can try it from this link in the option change my Apple ID and you have to log out from AppStore , FaceTime & iMessage in order to use your new iCloud account, make a iCloud backup first

https://appleid.apple.com