Hard drive won't free up space after deleting files

[morboz]

I have a Seagate ST500DM002 using windows 7.
it shows around 150GB free space, when I delete files from it (not to recycle bin), it still shows the same amount of free space, even after restart, any advice?

 

[Tmagic650]

This is a 500GB drive, right? How is it configured, as a boot or spare drive?