You can change the email address linked to your WordPress.com account on the Me tab (the person icon):
1. Open your Account Settings
2. Select Email
3. Enter your new email address
That will send a confirmation email to your new email address. You can follow the link in that email to complete the change.
Note: You will need to enter a unique email address that isn't already linked to another WordPress.com account. Learn more about your WordPress.com account email address.