You do not need to delete your files from your Restore Drive before you send it back to us, our Restores Team will automatically wipe all drives that they receive; however, it can be done if you wish to remove your data from the drive before sending it back, or you wish to keep the drive.
On Windows Machines, you only need to right-click on the drive itself, then select "Format" and hit "Start"
On Mac machines, there are two ways to remove files from your Restore Drive.
The first is to select the folder, file, or files, that you want to be removed and hold down Command + Delete.
The second is to select the folder, file, or files you want to be removed and right click and choose "move to trash".
In both instances, you will want to make sure to empty your trash before disconnecting your drives to ensure that the files are properly deleted.
(please note: The above refers to WD My Passport and 8TB WD My Book drives)