Old email address

See How to create a new Apple ID https://support.apple.com/en-us/HT204316. See the data implications below.

Some of these things may apply even though not changing an Apple ID: What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071

 Keep in mind that some things available under a first Apple ID will not be available under a new Apple ID. For example, you won’t be able to transfer anything purchased from the App and iTunes Stores to the new ID. And, there are other issues to be addressed.

And see what Eric Root says on this matter here https://discussions.apple.com/thread/251343949 and

what Winston Churchill says about it here: https://discussions.apple.com/thread/7452747

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The data issues mentioned above won't matter if you deactivate or delete your old Apple ID. As implied, you can deactivate or delete anApple ID account. Apple recommends doing the first for the obvious difference noted below.

How to deactivate your Apple ID account  https://support.apple.com/en-us/HT208503

If you request account deactivation, you'll receive a unique alphanumeric access code. When you're ready to reactivate your Apple ID, contact Apple Support, provide your access code, and we’ll help you reactivate your account. If you lose this code, we won't be able to help reactivate your account." 

How to Delete your Apple ID Account https://support.apple.com/en-us/HT208504 

“While your request is being processed, you can contact Apple Support with the unique alphanumeric access code you received, and we’ll help you cancel your request. After your account is deleted, Apple can't cancel the request, reopen your account, or restore your data.”

You can get additional information on both by signing in here: Data and https://support.apple.com/en-us/HT202667.

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But if you really just want to change change your Apple ID, here is some basic information on doing so.. But read the whole document linked below. And you will need to go to your Apple ID account (appleid.apple.com) for additional information. 

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

See this basic information:

1.   Sign out of iCloud on all of your devices, including your iPhone, Mac, Apple TV, and PC. If you use the Apple Music app on an Android device or use the Apple TV app a smart TV, sign out of those apps.

2.   Go to appleid.apple.com and sign in.

3.   In the Account section, choose Edit.

4.   Choose Change Apple ID.

You can sign out of iCloud on one of your devices, or you can sign out on all your devices to stop using iCloud (for sign out purposes, see 1 above). Before you sign out of iCloud, make sure that you archive or make copies of the information that you store in iCloud. When you sign out of iCloud, you can't access or use the following services on your devices or your Mac.

And see What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071

I suggest you change your existing Apple ID email address using the last part of donv's post. If you create/use a new Apple ID, you will lose access to some of your data and the purchases made with your existing Apple ID. You will also lose access if you deactivate or delete the existing ID.