can i build a setup that will overwrite the previouse installation...c# windows applciation..

It depends on what you are using for an installer. Since I use Visual Studio Express, it does not come with any built in support for generating a .MSI install file. Instead, I use the Nullsoft Scriptable Install System. It's pretty easy to use and is a lot more customizable than the built in .msi support that the pro version of Visual Studio contains. It will let you build installers that will install over top of your existing application, thus "upgrading" it, usually without any problems. But, be aware that for it to work properly you'll probably need to have any instance of the program that might still be running in the background disabled before your attempt to re-install it. Use the task manager to kill the process. http://nsis.sourceforge.net/Main_Page