Hi there Jackcob,
When go to the drive's folder through My Computer, you can right click and sort by data modified. That way you will see which files are the oldest and which are the newest ones. Then you can simply delete the ones that you don't need.
Apart from that, it will not hurt to check the HDD's health status out. You can run both short and extended DLG tests on it:
http://products.wdc.com/support/kb.ashx?id=8LwvIN
Let me know in case you have some more questions,
D_Know_WD