The website store allows you to upgrade a Lite licence to Premium and then to renew it for another year in the same transaction. Note that you cannot renew a licence until 90 days before it's expiry date.
To do this, first click the option Upgrade to Premium Edition:
This will change the licence in the store to Premium. You will then see the option to Renew as Premium Edition:
Once you have selected the Renew as Premium Edition option, you will see the price against the licence shows the upgrade cost as well as the renewal:
Read more about the store here.