G'Day Polly
Ignore the first answer - if you do format the drive you will lose
everything and have to reinstall everything.
Now what you can do: Download and install Unlocker from
http://ccollomb.free.fr/unlocker/ when you install it, it will put an entry in the context (right click) menu. Now find the file you cant delete and right click on it then left click on Unlocker, it will list all programs that have the file locked (so that it cant be deleted), now select Delete from the menu in the bottom left hand corner and click Unlock All. It will unlock the file and delete it (at least it has always worked for me, I have never had a file it cant get rid of). End of problem.