how to change the icloud email linked to my apple ID?

First understand that you can use either your iCloud Email or some third-party email as your Apple ID.

1. You cannot change the primary @icloud.com address on an iCloud account, but you can change the Apple ID - see 2. and 3.
2. If the Apple ID itself is a non-Apple third-party address you can change it, Change your Apple ID - Apple Support
3. If the Apple ID itself is an Apple @icloud.com, @me.com or @mac.com address you can't,
4. You can create up to three additional email aliases @icloud.com Use email aliases on iCloud.com - Apple Support