Bad Formating HDD

[jamalleze]

I used windows 10, then my pc got slow, and i dont like the 10 one, so i installed windows 7, not booted, i installed it over My Computer, now when i wanna boot my CD, to format my HDD, it just stands Windows 7, i got some options in the '' menu '' but cant use it, my HDD now have only 20 gb free space, and my Pc is kinda slow with this windows 7 to, pls help me out guyz, + i am on RAID on only, and my hdd is a 250 gb Seaget, thanks

 

[jamalleze]

I can send some pictures to, its not a problem, i just want this PC to go smooth again, because on windows 10 it lagged, my HDD lagged, now its better, but i think my old windows 10 is still on the HDD, so i want to delete it, but dont know how to completly format my hdd, manualy, because i can't boot it via CD, or via USB, thanks, sry for the bad english