How do you delete your first world on Minecraft?

I had this issue too, but don't fear! With just a little bit of effort, you should be able to get rid of your first world. Assuming that you are running on a windows system, go to your start menu and type %appdata% into the search bar. This should bring up a bunch of folders. Go to the one named .minecraft. Inside the .minecraft folder, there should be a folder labeled saves. Go into this folder and you will find the folders for your worlds. Find the folder that has the name of your first world, then delete it by right clicking and pressing delete. Hope this helps! (If you are on Mac, then I really can't help with this problem)

If you are on Mac, you can then go to Finder. Then press the Go menu on the Menu bar. Once a list pops up, hold down "option" and you should see the "Library" button pop up. Press it and a new window should come up. Go to the folder called "Application Support" then the folder "minecraft". In there, you should find the folder "saves" and you can "⌘-Delete" the folder that you want (the folder name corresponds to your world name). Then if you really want to delete it forever, you can right click on the trash can on your Dock then click Empty Trash. It should then ask if you really want to empty it. Press "Empty Trash". (This will erase everything in your trash that you have put in there.)

Hope this helps!