You need to create 2 copies of "C:\Windows\System32\ExplorerFrame.dll", one in a safe location as a backup and the 2nd one will be the one you modify.
Learn how to copy the backed up file back to it's original location replacing the modified file if anything goes wrong. Here is a couple of pages that might help,
Copy & Paste - in Windows Recovery Console
Peppermint3 - Create Live CD/DVD/USB To Use For Emergency Backup
In the Peppermint3 tutorial follow step A and B. Step C will show you how to open the File Manager to copy the files. Ubuntu is another Linux distro that I believe is popular.
As your not familiar with this type of stuff
after backing up the file and
taking ownership of the file in the original location I would recommend using either method to try and
copy the backed up file over the original one before replacing with your modified one. This way you can
confirm that you can replace the file before anything goes wrong.
Also if something does go wrong you may have to reset the computer using the button on the case so don't have any other programs running when you replace the files.
That's the most important info, knowing how to recover from a failed mod.