Move some to some other storage media or to an external HDD connected via a USB Port.
With the HDD nearing capacity you get restricted Page File activity which slows down dramatically the ability of the system to work as it was designed to do. Just because you have so much space available doesn't mean that you can use it all and maintain performance. Think of it like a car that can carry 2 tons of cargo it's can actually carry that much weight but it will take much longer to reach speed than if it was half full and a lot longer to slow down full as apposed to empty.
If you need to download large amounts of data off the net and you can not come anywhere near the volume that I download I have 8 X 400 GIG External Drives with less than 3% free space on them that are only turned on when I need something on that drive. I started off with 200 GIG Drives and have increased the size as I needed more space. When the 750 GIG drives get cheaper I'll be moving over to those as it will save a slight amount of space on my desktop and give me more storage space that I can use.
Whenever one of the HDD gets more than 80% full it starts to slow down and the longer that the system is used the slower things will be as that drive becomes more fragmented and continually slowing the system down further.
If you have lots of free space you can do as I do and leave the systems running indefinitely but the more room that you use on the HDD above a certain point the slower the system will become.
If you don't want to go with external Drives in USB Caddies you can add another internal HDD to your existing machine and move some data across from the primary HDD to free up some space though you'll be limited in the possible size that you can fit by the Computers BIOS upper size limit but that will cure your problem till you manage to fill up both drives again.
For Spy Ware Cleaners you can use these two the first is Ad Aware Se and is safe to use though it should be run in [b]Safe Mode[/b] to make sure that it picks up everything and removes it totally. After run once you always need to run again to make sure that you've actually removed the offending files and that there was noting else hiding under them
http://tinyurl.com/lvov4
Then this one is very good but you need to be careful
http://tinyurl.com/yrwy2
Spy Bot S&D is capable of picking up some programs that you are using things like Windows Defender and On Line Banking applications are the common ones as well as some downloaded software so if you see something that you are using you need to untick it from the removal list and then remove the rest.
As stated previously always run Spy Ware Scans in [b]Safe Mode[/b] and remember to run them several times to make sure that you've actually got everything. If you look at some application that you think that you need keep a count of the number of listings of it each time that you scan and you may decide that as this application grows in installed entries that it's not such a good program after all and needs to be removed.
Col