How to delete my iCloud account

An iCloud account is the same as an Apple account (ID). For information about how to delete your Apple ID account, read this support article --> How to delete your Apple ID account - Apple Support

Carefully and thoroughly read this for information about what happens when you delete your Apple ID account. For example:

"Make sure that you sign out of all your devices to avoid issues with apps that use your Apple ID account or iCloud. After your account is deleted, you can't sign out of iCloud or turn off Find My iPhone Activation Lock on your devices. If you forget to sign out, you might not be able to use your device when your account is deleted."