To change your associated email address login to your account on Runkeeper.com and then click on the gear icon located in the upper right hand corner of your screen to access your account settings.
Navigate to the email menu item on the left hand side.
Enter your updated email in the white empty box.
Next click the Add Another Email green button to save your changes. Lastly, you'll need to click the Make Primary link for the new email address to act as your official email for logging in!