Upgrade from free trial to paid

We have a few levels setup on our install of Membership. We have a free 30day trial too. If a member signsup for the 30day free trial, can that person upgrade to a paid account before their trial ends? If so how do they accomplish that? It seems like there should be a link that they click that would take them to a screen which allows them to upgrade when they are logged in. The site in question is http://horsewhispererusa.com/