If your world name has a space in it, you cannot teleport to it with the /world command. If you get a plugin called Multiverse, you can use that. With the plugin, you can do /mvtp "world name" and it will teleport you there. Or if you want to rename the world, do /mv clone "world name" newname and it will clone the world with the new name. Then you can delete the old world. If it says Multiverse does not recognize the world, do /mv import "world name" normal.