Added documentation for upgrading SPE.

Author: michaellwest

installation/README.md

@@ -86,6 +86,33 @@ The SPE module installs like any other for Sitecore. This approach is appropriat
 
 [Download](https://github.com/SitecorePowerShell/Console/releases) the module from the GitHub releases page and install through the _Installation Wizard_.
 
+## Upgrade
+
+We've tried to make upgrading SPE as seamless as possible. The following should provide you with some basic information on what to expect when upgrading.
+
+### From 6.x
+
+You should be able to install directly over the previous installation of 6.0+.
+
+* For Sitecore 10.1 and newer along with Identity Server you should enable the provided configuration _Spe.IdentityServer.config_.
+* For Sitecore 10.2 and newer you can leverage the IAR packages. There is still the need for *dacpac* deployments because SPE includes a security user and role.
+
+{% hint style="info" %}
+Using packages with the *Items as Resources* (IAR) files will require additional steps to remove database records that correlate with the contents of the _*.dat_ files. Refer to the Sitecore documentation when upgrading for the process to cleanup the databases. [This post](https://www.maartenwillebrands.nl/2022/02/15/sitecore-removing-iar-items-from-the-database/) may be helpful if you wish to take a more precise approach.
+{% endhint %}
+
+### From 5.x and older
+
+These versions used a different name for the assemblies and configs. You may find it easier to delete all files originally distributed with SPE before installing a newer version. Here are a few steps to consider:
+
+* Delete all files in the _bin_ and _App_Config/Include_ directories prefixed with *Cognifide*.
+* Delete _/sitecore modules/Shell/PowerShell_
+* Delete _/sitecore modules/PowerShell_
+
+Reference the original SPE package (if available) to identify if any other files were included.
+
+Sitecore items in the content tree will potentially shuffle around into their new location. Be sure to backup your custom scripts first.
+
 ## Troubleshooting
 
 See the troubleshooting section [here](../troubleshooting.md)