Do I delete disk1s1 in Disk Utility?

Thanks for replies to my previous post by leroydouglas, HWTech and TheLittles, I have deleted my HD but...

Having now gone back into Disk Utilities, I find that disk1s1 is as full as my HD was. As I'm getting rid of my computer, how do I delete all this as the Erase button is not lit up? Or what is this file for? Is it readable by anyone else?

Thank you