If you have a yearly licence, it will renew every 12 months. Normally this will happen automatically – you’ll get an email a week before to remind you that it’s going to happen but you don’t need to do anything to ensure it happens.
However, occasionally the renewal might fail – for instance, if you’ve changed your bank card since the original purchase. In this case, you will need to renew manually.
To do this, just go to the Account on the website, https://pluginrepublic.com/my-account/, click the Subscriptions tab and click ‘Renew’ against the plugin name.