Update-SqlWhoIsActive is pretty much an alias for Install-SqlWhoIsActive. They both do the same thing.
dbatools is a free PowerShell module with over 180 SQL Server administration, best practice and migration commands included.
Get-HelpFrom PowerShell, execute Get-Help Update-SqlWhoIsActive -Detailed for more information on this function.
Source CodeWant to see the source code? View Update-SqlWhoIsActive.ps1 on GitHub