Otherwise, you'll need to format to "Mac OS Extended (Journaled)" for El Capitan and earlier. When you're sure about your decision, click "Erase" and confirm. Finally, quit Disk Utility and select ...

Version 10.11 of the Mac OS X operating system, named after a rock formation in Yosemite National Park. Introduced in 2015, El Capitan includes faster performance and a raft of enhancements ...