how do you change your (mac/me/icloud) email address

You cannot change an iCloud email address unless you create a new iCloud account. You can, however, create an email alias, which is an alternate email address that will receive incoming email in your existing iCloud email inbox. To do this, see http://support.apple.com/kb/PH2622. Just keep in mind that once you creat an alias, you can't later use this to create a new iCloud account or move it to another account, even if you delete the alias.