TCPOptimiser should sort the problem out.
Quick and simple.
Start the program with administrative permissions: right-click on the program, choose "Run as administrator" -> OK
Choose your maximum connection speed (as advertised from your ISP) in the slider bar.(or move slider fully to the right if over 100Mbps connection)
Choose your Network Adapter that connects you to the Internet (or tick "Modify all network adapters")
Pick "Optimal settings" from the radio-buttons near the bottom of the program
Click on the "Apply changes" button, choose to create backup and log, and reboot when prompted