3 hard drives. Need help getting Windows off the other two without formatting them

[TheYooper]

Hey guys this is my first post on my new account (forgot my login to my other account lol). So i just recently picked up a computer on craigslist that was pretty basic and has windows 7 professional. So i wanted more storage for steam games so i dropped in a 500gb hard drive from an old computer. I also wanted a back up hard drive for all my programs and valuable stuff in case i wanted to transfer to a new computer or in case this one died so i dropped in a 3rd 250gb hard drive. But i have two problems, one both the second and third hard drive have windows 7 installed on it and i cannot get "permission" to delete the files off of them. Second I don't know a lot about computer software only hardware and i don't know how to set up my third hard drive as the back up hard drive i wish to have. Thank you for taking your time in reading this!

 

[Solandri]

If you don't need the data on the drives, just format them.

If you need the data, you have to take ownership of the files (assuming they're not encrypted - if they are you need to boot the drive in the original computer and remove the encryption).
https://technet.microsoft.com/en-us/library/Cc753659.aspx

For the backup drive, use a good backup program. Macrium Reflect and EaseUs have free versions that are sufficient for most users, and are relatively easy to use.