如何从旧补丁中重新启动文件？

I have a basic MSI project in installsheild 2012. I want to be able to install a patch (major upgrade) which backs up the current configuration files when it is installed in way so that when I remove the patch that the old configuration files are re-instated. At the moment when I update these files are deleted.I have a basic MSI project in installsheild 201