0.5.1 doesn’t have a database. That’s basically what was implemented into 0.6, which set up the server to have more features added and allow people to create characters and such. (Note I say set up the server to have more. 0.6 doesn’t have these things.) 0.5.1 is just click and play basically. Download the Easy World changer to change worlds. You will have to log on and off to switch though.