Hey there! In the updates Tuesday the devs did away with commands such as /worlds, it can all be done through the file manager now! There should be a upload button in the file manager, and to change what world you want to spawn in on you have to change the level name to the world you want to spawn in on in settings.
To be able to continue to teleport in-game you will need to use a plugin such as Multiverse. Unfortunately, multiverse/plugins in general are not my strong suit so I can't offer much help with how to use it other than to tell you to look up tutorials/contacting the creator.