When you signed into the wifi, it probably gave you a confirmation screen of some kind - usually with a link to manage your connection/see how much time you have left/that kind of thing. If you don't remember that page's address (and who would?), then you can either wait for your free period to time out, when it will prompt you to sign on again, or you can call the front desk and ask them if they can reset your wifi connection because you'd like to switch to the faster tier.