Just head over to your desktop and open up file explorer, navigate over to your C:\ drive and right click it. Chose properties and click on "Disk Cleanup". Let it do its thing, you should then get the Disk Cleanup box. Check off what you want cleaned up and enjoy your extra space.
In my case, after running disk cleanup I now have 93GB free space. For now, I will take as much as I can, would like to see 256GB SSD become a standard for the Surface Pro.
Also I have picked up a 64GB microSD card to store pictures, music, documents and sync my Skydrive.