I can write a little guide to do this tomorrow if you like. I suspect it’s a permissions problem, which should be easy to overcome.
I’ve not tried this myself, but now have a reason to.
The last time I looked there are two separate folders, one with the clean textures in, the other with the old. You shouldn’t need to delete anything, just copy over the files inside the folder, not the folder itself, into the destination, and overwrite the existing files.
The two backup copies allow you to flip flop between the two versions at will. I suspect the permissions problem could be sorted by opening a copy of Explorer with admin rights.
Open a copy of Command Prompt, but run as Administrator. From that Window type:
Explorer.exe .
That should open a new Explorer window, but is now “elevated”. The “.” is not a typo, it just tells Explorer to open at the current location. Then try copying the relevant files from that window.
As I say, I’ll play with this tomorrow, and take some notes.