macbook pro 10.7.2 how do I delete the 750.16 GB toshiba disk

[appleukabc]

Hi all I'm new to forum and new to macs so need your help please I've purchased a new macbook pro 10.7.2 with mountain lion and I want to factory restore it I have done the mac hd erase but evrytime I go to erase the 750.16 gb toshiba disk it says it can unmount disk is there anyway to delete this so I can do a fresh install from my lion usb installer any help would be much appreciated cheers

 

[Weaselboy]

It sounds like you did a command-r boot to the Recovery HD partition? That will not allow you to erase the entire drive since you are booted to it.

Instead plug in your Lion installer USB key and hold the option key when you boot. This will bring up a selector screen where you can pick the USB key to boot from. Then you can use Disk Utility to format the drive.