I’ve just needed to upgrade a web part installed in our SharePoint farm.  I could have gone to Central Administration, retracted, then removed the solution, but I wanted a quicker procedure.

I originally installed the web part using the Add-SPSolution PowerShell command.  I first attempted to update the web part using Add-SPSoultion -LiteralPath %path to updated wsp file%, but received the error “A solution with the name …. already exists in the solution store.”

I realised I needed to use the Update-SPSolution PowerShell command.  This required two extra parameters, the name of the web part solution to be updated and the -GACDeployment parameter.  When I ran this command, the existing web part was automatically updated using a SharePoint timer job.