Please click on the links and read the documents -->
Change your Apple ID - https://support.apple.com/HT202667 - "Follow these steps to change the email address that you use as your Apple ID." Plus special instructions if you want to change your Apple ID to an @icloud.com address. You may also wish to turn off "Find My" before changing information and turn it on again afterward.
"If you try to change your Apple ID to an @icloud.com email address that was created within the last 30 days, you will be asked to try again later.
If you see a message that the email address you want to use isn't available or is already in use, check that you or a family member aren't already using that email address with a different Apple ID. If a family member is using that email address, remove it from their account then try to use it."