Before you unsintall an application, it's advised to use a program that can monitor the performance of your computer as well as every process that is running on it. In this matter, I suggest you download and use Process Lasso. Using this tool, you can monitor the activity of your computer and find out exactly what process is making your computer's performance to drop.
If still want to unisntall a program, you just simply need to go to Start > Control Panel > Add or Remove Programs (Windows XP) or Programs and Features (Windows 7) > select the application and press Uninstall. If you wave problems uninstalling a program in this way, use Revo Uninstaller. This tool is specially designed to remove any application from your computer by force.