How to downgrade windows to Windows 7

You might want to give Classic Shell a try - it's free and alleviates a lot of the pain of Windows 8.

http://www.classicshell.net/

If you want to use the downgrade rights, see here

www.microsoft.com/.../downgrade_rights.aspx

Note that all software support is only for Windows 8.1, so you're on your own with Dell if you use 7.

Downgrading is not free however.

• Use genuine Windows media and a corresponding product key for the version of Windows that is eligible for downgrade. The media/key should come from a previously licensed product from the OEM or retail channel.
• End users who are licensed separately through Microsoft Volume Licensing (VL) may provide their VL media and key to a system builder to facilitate the downgrade on their own systems.
• Insert the downgrade-eligible version of Windows media and follow the installation instructions.
• Enter the product key.
• If the software was previously activated, it cannot be activated online. In this case, the appropriate local Activation Support phone number will be displayed. Call the number and explain the circumstances. When it is determined that the end user has an eligible Windows license, the customer service representative will provide a single-use activation code to activate the software. Please note that Microsoft does not provide a full product key in this scenario.
• Activate the software.

  Downgrade rights for Windows software

  The following OEM versions of Windows software are eligible for downgrade rights.

  Windows 8.1	Windows 7
  Windows 8.1 Pro includes downgrade rights to: Windows 7 Professional Windows Vista Business	Windows 7 Professional and Windows 7 Ultimate include downgrade rights to: Windows Vista Business and Windows Vista Ultimate Windows XP Professional, Windows XP Tablet PC Edition, or Windows XP x64 Edition Note Other OEM Windows 7 versions (for example, Windows 7 Home Basic and Windows 7 Home Premium) do not include downgrade rights.

See here:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/a-clean-install-of-windows-7/