How to delete or change existing iCloud email?

Not sure what you mean? If you mean changing the primary email address used with your AppleID for iCloud, then see -> Change your Apple ID - Apple Support

If you mean changing the xxx@icloud.com email address of your iCloud account email, then that cannot be edited. You can create an alias to use instead. But the iCloud email address you create with an iCloud account cannot be altered.

mlp327 Said:

"How to delete or change existing iCloud email address?"

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Create and Use a New Alias:

If you wanted to, create a new Alias. Then, turn off your current one. Go Here: Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support. Everything would be kept, but your eMail would be different. Trash all this junk, seeing if you no longer get it. You cannot turn off your current iCloud Account.