Internet Cyclone is a comprehensive internet connection (TCP/IP) optimisation tool for Windows XP and earlier.
The program looks a little intimidating when you first launch it, with multiple options crammed into a tiny interface, but it's actually quite straightforward. At a minimum, all you have to do is choose your connection type, Internet Cyclone will select the appropriate settings for you, and you can click Optimize to tweak your connection accordingly.
The program supports three automatic optimisation modes that you can try, if the first doesn't help. Or you can choose Custom Mode and select the appropriate settings for yourself, if you're confident in doing that. (If you're uncertain what they mean then the Help file offers a little guidance, although it shows its age by paying great attention to the appropriate settings for Windows 98.)
Please note, in this demo version of the program only MTU, MSS, TTL, RWIN and NDI settings are saved. Purchasing a licence to the program will unlock its additional settings and features.