As a design student, once your free trial has expired you can upgrade to a paying membership and claim your coupon code discount to gain access to your projects and libraries. All projects and library folders created within your trial will be available to you.
Step 1: Open your profile my signing in and selecting "Account Information". Click the green link "Change my Subscription" on the right-handside.
Step 2: A popup will come up as per the screenshot below, choose the orange button "Change my Plan".
Step 3: Select the membership you would like to buy. Note that if you want to pay yearly please select the "Pro: $490 / year" link as per the circle below
Step 3: A checkout page will open, as per the screenshot below. Input your coupon code in the space provided and click "Update" next to it to claim your discount.