You can probably reclaim a lot of that disk space through removing old windows updates and maybe even installation files for SP1. There are tools available for this if you google for it. My winsxs folder shrinked by 12GB when I did this.
If you have a valid key for Windows you can use that to gain access to the Windows 10 iso that you can create an USB key and do a clean install with it. Windows 10 activates if you had a valid Windows 7/8/8.1 key activated to your MAC adress earlier, at least it did for me.