Hi
Check out this video....
Remember this will wipe everything on your computer.
If you have data, music, photos etc. on you computer that you can't afford to lose you may want to make a Ubuntu disk on another computer and use it to boot your computer and copy your stuff to DVDs or an external hard drive.
Download Ubuntu Desktop | Download | Ubuntu Ignore the contributions info and find "Not now take my to the download".
Note: You will have to use ImgBurn or a similar program to make a bootable disk from the ISO image file.
When you boot to the disk don't select the install option just boot to the disk and you will be able to access your files and copy them.
Mike