At any point in time, you may opt to upgrade your account. Select the plan appropriate to your needs. You can do this in the account section of your profile.
Step 1 - You’ll see the option, “Upgrade Today”.
Step 2 - Then select the appropriate currency.
Step 3 - When upgrading, select either of the available plans, Plus, Premium or Lifetime and click "Upgrade".
Step 4 - Enter payment details, and then click Subscribe. To get a discounted rate, you might want to be billed yearly instead of monthly.