Go to your saves folder in your .minecraft folder.
To get there you must type %appdata% in your little bar thingy (I'm using windows so I click on the windows icon and type %appdata% in the search bar.)
A folder named Roaming should appear.
Click on it and (For me at least) at the top there should be a folder named .minecraft. Just go in it and go to saves and you got it!


Sorry but I don't know how to do it on Macs (Since I don't have one) :P