When you log in, go to My Account area in the top right corner of the page and click on the 'Upgrade Now' link to access upgrade options. Note that you'll be transferred to a secured payment page to complete your transaction. You'll be invited to log back into your account where your new upgrade options will be visible.
When you are upgrading be sure to use the email id that you used to first open your account. DO NOT use any other emails. If you want to change the email associated to your account this can be done in your account settings it should not be done when upgrading or signing in.
You are responsible for remembering your email id and password. We cannot retrieve this information for you. If you have forgotten your password, see this FAQ.