Turn on your computer so that your current version of Windows starts normally, and then do one of the following:
If you downloaded Windows 7, browse to the installation file you downloaded, and then double-click it (often identified as an Application file under the Type column).
If you have a Windows 7 installation disc, insert the disc into your computer. Setup should start automatically. If it doesn't, click the Start button, click Computer, double-click your DVD drive to open the Windows 7 installation disc, and then double-click setup.exe.