Add Support For Upgrading Site

[RichMercer]

Add a switch to Install-TelligentInstance to allow upgrading of an existing site.

[afscrome]

If you're talking about a true upgrade of an existing instance, I think this should be a separate command, rather than shoehorned into the install command:

Upgrade-TelligentInstance -NewVersion 9.1 -Name FooBar or Get-TelligentInstance 9.1 | Upgrade-TelligentInstance -NewVersion 9.1