• Go to Start --> Run
• Type cmd in the input box and press Enter
• Now naviagate to the directory where the DLL is present and type “regsvr32 /u name_of_the_file.dll
• Here, the command regsvr32 is used to register or unregister the DLL and /u in the above command commands the CMD to unregister that DLL.

Thus the DLL file is unregistered. However, it should be remembered that this can bring several changes to your computer and taking a backup of these files is recommended before doing this.