Windows hard drive - mac

My windows pc has been playing up recently, and i know its a problem with the hard drive, because the only other available pc in the house is my imac, i was wondering how to delete files off the hard drive??!!! i have recently bought a device that allows me to connect my hard drive to the imac but i cant seem to delete anything off of it as it seems to be locked, is there an easy way of unlocking these items so i may remove them ??? (HARD DRIVE ---> 'WESTERN DIGITAL') ??

Unless you need to keep the drive as-is for some reason just reformat it with Disk Utility.
It's probably formatted as NTFS which OS X can read but not write to without 3rd party software.

You can use a 3rd party App such as NTFS Mounter to access and manage the disc without reformatting. I've been using it for a while and it works fine.