Open your PP, then go to ADD/EDIT Email and add a new email and verify it and make it primary. And then remove the other email.
You can not change your email address , if your account is limited. Other wise scroll the mouse on "My profile", below you will see the option "Add/Edit" option.
You can change your email address in paypal in "My Profile" section. You may also add more than one email address as well.