To uninstall Windows 7 from your computer and revert back to the previous operating system you should know how was Windows 7 installed. Given below is the list of scenarios and steps for uninstalling Windows 7’s installation.

Scenario 1:

Windows 7 was installed as a new installation over an earlier version of WindowsThis stands true when you used the Windows 7 installation media to install Windows 7 to the same hard disk drive on which you had Windows XP, Windows Vista, or another version of Windows 7 installed. This applies to situations when you upgraded to Windows 7 using both the Upgrade media and the Full product media.
in such kind of installation the Windows 7 installation would have created a Windows.old folder that contains your previous operating system and personal files. The Windows.old folder is in the root of the Windows partition. To revert to this previous operating system follow the following steps:

  1. Start the Windows Recovery Environment. Put the Windows 7 installation disc in the DVD drive, and then restart the computer. Press a key when you are prompted to restart from the disc. In the Install Windows window, select a language, a time, a currency, a keyboard input method or other input method, and then click Next. In the Install Windows window, click Repair your computer. In the System Recovery Options window, click the version of the Windows 7 operating system that you want to repair, and then click Next. In the System Recovery Options window, click Command Prompt. The Command Prompt window opens, and it displays the command prompt. The command prompt is where you will type the commands that are described in the following steps.
  2. Move the Windows 7 folders to a new Win7 folderType the following commands and press ENTER after each command:C: Md Win7 Move Windows Win7\WindowsMove “Program Files” “Win7\Program Files” Move Users Win7\Users Attrib –h –s –r ProgramData Move ProgramData Win7\ProgramData Rd “Documents and Settings”
  3. Copy the contents or move the contents of the Windows.old folder.Type the following commands and press ENTER after each command:move /y c:\Windows.old\Windows c:\ move /y “c:\Windows.old\Program Files” c:\ move /y c:\Windows.old\ProgramData c:\ move /y c:\Windows.old\Users c:\ move /y “c:\Windows.old\Documents and Settings” c:\
  4. Restore the boot sector for the previous Windows installationType one of the following commands at the command prompt, as applicable.
    • Type the following command, and then press ENTER:D:\boot\bootsect /nt52 c:When the previous Windows installation was Windows Vista
    • Type the following command, and then press ENTER:D:\boot\bootsect /nt60 c:
  5. Restore the Boot.ini file for the previous Windows installation of Windows XP or of Windows 2000Type the following commands and press ENTER after each command:Attrib –h –s –r boot.ini.saved Copy boot.ini.saved boot.ini
  6. Close the Command Prompt window, and then click RestartType the following command at the command prompt, and then press ENTER:exitClick Restart to restart your computer.

Scenario 2:

Windows 7 was installed on a computer that did not have an operating system installedIn this case Windows 7 was installed on a blank hard drive, and there is no previous operating system to which the installation can be reverted

Scenario 3:

You upgraded from Windows Vista to Windows 7You installed Windows 7 on a Windows Vista-based computer, by inserting the Windows 7 installation media and selecting the Upgrade option. Then, you upgraded from Windows Vista to Windows 7. In this case Windows 7 was installed on a blank hard drive, and there is no previous operating system to which the installation can be reverted

Scenario 4:

You installed Windows 7 on a multiboot systemYou have installed Windows 7 on a separate partition, and kept the earlier version of Windows on your computer. In this case follow the following steps:1. Open System Configuration by going to Start -> Control Panel -> System and Security ->Administrative Tools -> System Configuration.2. Click on the Boot tab and click the listing for Windows 7.3. Click Delete, click OK, and then click Restart.