When I try to upgrade to the newest version, v1.0.0-beta4, I am getting the blow error. I am also attaching a screenshot.
Index (zero based) must be greater than or equal to zero and less than the size of the argument list.

There are issues with PoweShellGet/PackageManagement when it comes to pre-release packages. Try this:
Install-Module posh-git -AllowPrerelease -Scope CurrentUser -Force
If that doesn't work, manually remove the current posh-git module folder and try the above again.
I had to run Remove-Module posh-git first then remove the folder and then the command above worked. I will check for a bug on PowerShellGet/PackageManagement and comment there. Thank you for your help.
Most helpful comment
There are issues with PoweShellGet/PackageManagement when it comes to pre-release packages. Try this:
If that doesn't work, manually remove the current posh-git module folder and try the above again.