4 year old iMac remove everything and start fresh

[blasto333]

I have an iMac that is 4 years old and recently upgraded to a laptop. I would like to wipe the system clean and reinstall everything again (including the operating system). I booted into the recovery partition and attempted to erase "Macintosh HD" but it said the volume could not be unmounted.

I know I could delete the user accounts; but I want it completely erased so it runs a bit faster.

Is there any way to do this without the CD/DVD that came with it?

 

[Weaselboy]

You can follow this guide to do a fresh install with Yosemite.

 

[akm3]

Will a fresh install of Yosemite break a Boot Camp installation?

 

[Weaselboy]

Will a fresh install of Yosemite break a Boot Camp installation?

I don't use Bootcamp, but I have seen several posts in here that it does in some cases. Others is works okay.