To change your password login to your account on Runkeeper.com and then click on the gear icon located in the upper right hand corner to access your account settings.
Navigate to the Password menu item on the left hand side.
Enter your Old password then enter New password and re-enter to Verify new password. Password must be 6-8 alpha-numeric characters (no special characters!). Make sure you click the Change Password button to save changes.
NOTE: You will need to update the password you have entered in your Runkeeper app settings so that your new activities can be uploaded to your web account!