1. Open the %systemroot%\system32 folder. %systemroot% is the folder in which Windows is installed. For example, the %systemroot% folder is C:\Windows.
2. Right-click Wuaueng.dll, and then click Properties.
3. Click the Details tab, and then locate the file version number.
Note: The latest version of the Windows Update Agent for Windows 8.1 is 7.9.9600.16422. The latest version of the Windows Update Agent for Windows 8 is 7.8.9200.16693. The latest version of the Windows Update Agent for Windows 7, Windows Vista, and Windows XP is 7.6.7600.256.