Try starting with
Ad-Aware and
Spybot. Both of which are free to download and install, and work wonders to remove and protect you from malware.
You can also download and install
Microsoft 's Defender program, if you can navigate the web with the problem computer.
If any or all the above fails, you can try removing it manually by following the instructions
here.
As stated in the link above, one of the biggest problems with malware is it's ability to re-generate it's own executable files if you're able to delete the current set. They will also rename them each time to some random name, as opposed to an easy-to-locate "popcorn.exe". Names like hsdrrt.exe, or wtghtqp.exe.
Good luck, removing this stuff can be extremely frustrating.
Randy