A feature with ID has already been installed in this farm. Use the force attribute to explicitly re-install the feature.

Steps through Visual Studio 2010:

1. Go to your Features in your project.
2. Open the feature.template.xml file add AlwaysForceInstall="TRUE" to the below tag Now try to deploy the code.



Steps through PowerShell:

In PowerShell, you can use the -Force parameter of the Install-SPSolution commandlet in order to force the installation of a solution:
"Install-SPSolution -Identity -GACDeployment -Force "