How to delete multiple Minecraft worlds on Xbox
In case you are already loaded into a world, click on the options button and select quit to the main menu.
Now, in the main menu screen, enter the Worlds menu and click on the pencil edit icon that is next to the world that you would like to delete. This will take you into the Edit World section. Here, under the Game tab, scroll down to the very bottom to find the Delete World option.
Keep in mind that this deletion cannot be reversed, so you may want to double-check if you are indeed in the right edit world menu, since you would not want to do away with hundreds of hours of effort of you and your friends all with one single elementary mistake. Once you are absolutely certain, click on the Delete World option.