How to update existing WSP in sharepoint Farm using PowerShell

In this article we all learn about updating the new WSP with out retracting the existing WSP. 

Using Power Shell we are  updating the new WSP with new custom changes in our  SharePoint Farm. 

Take the backup of existing WSP,it may useful in future. 

here we can able to find the article How to download WSP file Central Admin Syntax: 

Update-SPSolution –Identity yourwspname.wsp –LiteralPath "WSP Path" –GACDeployment 

Example: 
Update-SPSolution –Identity DotNetSharePoint.wsp –LiteralPath "C:\DotNetSharePoint.wsp" –GACDeployment