How Do I Delete Multiple Downloads of the Same Document?

I purchased two eBooks, and I had several problems with my first downloads (lost wireless connection once, and received multiple error messages on repeated tried to download. I ended up with three copies of one book and two copies of the other. I used the delete command on the eBook with two copies, and the computer locked (Dell 8700 running Windows 7). On reboot, both copies were still in the library. How do I delete the duplicate copies and keep one copy of each eBook?