Uninstallation and Retraction of a Solution in SharePoint 2010
Using STSADM:
stsadm -o retractsolution -name solutionName.wsp -immediate
stsadm -o deletesolution -name solutionName.wsp
Using PowerShell:
Uninstall-SPSolution -identity solutionName.wsp
Remove-SPSolution -identity solutionName.wsp
