Hi there Mixalhs212,
I believe this is attached as a secondary drive right?
Well, you can just go to Disk Management and repartition and reformat it. Keep in mind that you need to back up all the data stored on it after that.
If you are having some difficulties with that, you can use some third party HDD wiping tool. Check this one for example:
http://www.tomshardware.co.uk/answers/id-1711997/software-wipe-hdds.html
This process will fill in zero value in each sector of the drive. The data would be unrecoverable.
Let me know in case you have some more questions,
D_Know_WD