I have used this site for Windows 10 and 11; it gives step-by-step instructions to change user name..
https://www.lifewire.com/change-user-folder-name-in-windows-10-5114140
the 350/350 is the most sent receive your computer can get; since you stated this is Wi-Fi I would turn off Wi-Fi and test with internet cable to the modem to test lan speed as Wiganken stated.