How to delete the old .NET SDKs

dotnet --list-sdks
dotnet --list-runtimes

Change the version and run:

version="3.1.29"
sudo rm -rf /usr/local/share/dotnet/sdk/$version
sudo rm -rf /usr/local/share/dotnet/shared/Microsoft.NETCore.App/$version
sudo rm -rf /usr/local/share/dotnet/shared/Microsoft.AspNetCore.All/$version
sudo rm -rf /usr/local/share/dotnet/shared/Microsoft.AspNetCore.App/$version
sudo rm -rf /usr/local/share/dotnet/host/fxr/$version