It is not advised to delete an app if it's installed on your computer. By doing this, some associated files might remain in the system. To properly remove it from your computer, you need to uninstall it first. Go to Start -> Control Panel -> Add/Remove Programs (Windows XP) or Programs and Features (Windows 7) select the program and hit Uninstall. If you don't succeed, try using Revo Uninstaller. This tool will force any application to unsintall by removing any trace of it's presence from the system.