wsl command doesn't have --set-version option in my powershell

I tried to install new version of WSL meant WSL2 according to the installation instructions documented by Microsoft but the wsl command doesn't have --set-version option in my PowerShell to complete instructions while the WSL Ubuntu 18.04 is already been installed. I ran PowerSell as administrator in my windows 10 build 1903. How can i fix this? any help will be appreciated.