To take the backup of the WSP in SharePoint 2010,
Run the following commands from PowerShell where SharePoint 2010 is configured.
Add-PSSnapin Microsoft.SharePoint.PowerShell
$farm = Get-SPFarm
$file = $farm.Solutions.Item("mysolution.wsp").SolutionFile
$file.SaveAs("C:\WSPs\mysolution.wsp")
This saves the wsp to the desired location. The WSP can then be deployed like any other solution.