Steve
I would go to speedguide: https://www.speedguide.net/
Go to the tcp:optimizer which is under broadband, read the faq, then download the optimizer.To find your optimal RWIN use the DSLnuts calculator: http://www.dslnuts.com/bitsbytes.shtml You can use this test to determine how your tweeks are working: http://www.broadbandreports.com/tweaks
Don't forget to back up your registry.
Everybodys connection is different, you might hit the right RWIN number right away, or like me it might take 10 or 12 hours of tweeking to get the right settings, but either way it is worth it.
GOOD LUCK Let me know how it goes