Just a simple format of each of the drives will take care of that when you go to reinstall windows.
Follow these steps. This will wipe all data from the drives. Make sure you save anything you want to keep to USB or Cloud.
If the entire hard drive not show as unallocated space, then delete all partitions on the hard drive until it's unallocated (see screenshot below). Select a partition and click on the "Delete" option for each partition. Do this for each of the drives you have installed.
- Option 1:
Click on the "Next" button. The installation of Windows 10 will begin. All the required partitions are created automatically during the install.
- Option 2:
Select the "New" and "Apply" buttons.
Click on the "Next" button. The installation of Windows 10 will begin.