do the below steps after you install the OEM version
Here's how to begin:
Open Windows Anytime Upgrade by clicking the Start button . In the search box, type anytime upgrade, and then, in the list of results, click Windows Anytime Upgrade.
Follow the instructions on each page.
When the upgrade is complete, you will have a new edition of Windows 7 running on your computer.
Windows Anytime Upgrade will only allow upgrades from a 32-bit version to a 32-bit version or from a 64-bit version to a 64-bit version. You can't upgrade from a 32-bit version to a 64-bit version with Windows Anytime Upgrade, for example. For more information about 32-bit and 64-bit versions of Windows, see 32-bit and 64-bit Windows: frequently asked questions.
Windows Anytime Upgrade isn't available in all editions of Windows 7, such as Windows 7 Ultimate edition.
Windows Anytime Upgrade is only available for online purchase in Australia, Belgium, Canada, Germany, France, Italy, Japan, the Netherlands, Spain, Sweden, Switzerland, the United Kingdom, and the United States.