How to delete old and replace with new Apple account?

If you simply want to change your Apple ID email address to a new one, then follow the steps here:

Change your Apple Account primary email address - Apple Support

If you do want to delete all your data associated with your current Apple Account then read the information provided here very carefully. Pay particular attention to the part that says to sign out of your account on all your devices. If you don't follow that step, your device will be locked to that Apple ID and you will not be able to sign out since the password for that account will no longer work. There are many more consequences where data loss will occur, so make sure you understand:

How to delete your Apple Account - Apple Support

Delete the Apple Account from where?

If this is an iPhone or iPad you’ve recently acquired, and if this involves Activation Lock, then contact the seller.

Request the seller release the lock. That can be done remotely.

Activation Lock is intended as a theft deterrent, and is intentionally difficult to bypass.

You’ll need the person holding the lock to release it, or provide convincing proof of ownership to Apple.