How to actually change TCP Window size in Windows 10

Question

One of my customers asked me to perform a test with a TCP Windows size that is bigger than the standard in Windows 10. With this test they want to see if they can increase download speeds for a specific server.

Customer has an office in Asia with Windows 10 workstations downloading files from a server in Europe. The Asia office building has a 700mbit up and down fiber connection.

Site in Europe had a 1000mbit up and down fiber connection.

The problem is the latency between the two countries is never lower than 260 to 300ms. There is no way around it. This results in download speeds not going faster dan 2mb/s for downloading the files from the European server. Downloading a file from a server in Asia is very fast.

My question:

What is the exact registry items I need to add or change to modify the TCP Window settings?

I have tried the tcpwindowsize key in HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Tcpip\Parameters

You should be able to use "Get-NetTCPSetting" to see if any changes were made.

However I don't see anything changing so I'm confused on what I need to change to perform this test, all I need to know is what needs to be set.