A few years ago I did this.

The best way is by first setting yourself up with a password manager like 1password or bitwarden first on all the sites you log into. That way, you have a list of sites you then need to change your email on. But in the end, the tip and trick is "one by one."

Then set up email forwarding from the old email to catch any stragglers. After a few years, the old email is obselete and even all the spammers know your new email.