By default, a built-in system account "TrustedInstaller" has ownership and full control of all system files in Windows Vista, Windows 7 and later OS, so you need to take ownership and assign full permission to yourself before modifying or replacing the system file.

Once you take ownership of a file or folder in Windows, if you go back to its Properties and try to change the owner back to "TrustedInstaller", you'll be surprised to see that "TrustedInstaller" is no longer present in the users list. To bring back the built-in system user "TrustedInstaller" and set it as default owner of a file or folder do the following:

1. Go to the folder which contains the file or folder for which you want to restore ownership to "TrustedInstaller". Right-click on the file or folder and select Properties.
2. It'll open its Properties window. Now go to "Security" tab and click on Advanced button.
3. It'll open a new window. Now go to "Owner" tab and you'll see that the owner would be set to your username and "TrustedInstaller" would not be present in the list as we mentioned above.
4. Don't worry. We'll add it manually. Click on "Edit" button:
5. It'll open another window. Click on "Other users or groups" button.
6. Now type NT SERVICETrustedInstaller in "Enter the object name to select" text box and click on OK button as shown in following screenshot:
7. It'll immediately add "TrustedInstaller" to the users list. Click on Apply button.
8. Windows will show a message box, click on OK button to close it. Again click on OK button in all opened windows and you have successfully restored "TrustedInstaller" as default owner of the file or folder.

You can check and confirm the owner by opening the file or folder Properties and you'll see that "TrustedInstaller" has become the owner of that file or folder again