Can I change my iCloud email account

No, you can only change an account alias.

"Note: You can’t delete or turn off a primary iCloud Mail address. You can’t use an alias to create a separate Apple ID, and an email alias can’t be converted to a primary iCloud Mail address."

Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support

Easiest thing is to create the new Apple ID and still transfer the old data to the gadget storage and upload it to the new iCloud account as well as upgrade the iCloud storage too.

Note, however, that anything purchased with an ID remains permanently tied to that ID. If you abandon the old account then you lose the items.