Click the My Orders tab on the left side of the page

Click the gear icon for the order you would like to change and select "Change Order"

Select "Change tickets"

Click "Edit" for the ticket you would like to transfer to upgrade

Select the ticket type you would like to upgrade to 
*Please note that you will be charged for any difference in price, requiring you to enter in your card information

Fill out any required information and click "Update Information"

Click the Pay button at the bottom of the page, which will tell you your total (if applicable)

You will then be emailed a copy of your new receipt, reflecting these changes!