In order to find out if your Ubuntu or other WSL linux installation is running on WSL1 or WSL2, open a Powershell and run
wsl --list -v
This will show you all WSL installations and the associated WSL versions:
PS C:\WINDOWS\system32> wsl --list -v NAME STATE VERSION * Ubuntu Running 1
As you can see, the Ubuntu VM is running WSL VERSION 1.
Go to the WSL2 installation page for instructions on how to upgrade to WSL2.