To change your world’s name, go to the World tab and click into the Name field. A keyboard will appear for you to type in your desired name. You can even use your laser pointer to select a position, and highlight text to easily delete.
Let's Choose a unique name, mine is going to be “Laex’s Parkour Balloon Fight”
You can change the name of your world at any time, this immediately affects the published version of your world.