Replace Explorer.exe With Another?

i just downloaded a windows 7 theme from deviantart, however the start menu doesn't chance and i asked the author of it and he tells me i need to chance the explorer.exe with the one that came with his theme.

But i can't replace it because windows 7 isn't allowing me to do it because of lack of rights. wich i should have since im the only user on my computer and with fully administrative rights.

I also have taken ownership of the file, but i still cannot replace the original explorer.exe file

here is a link to the theme how it should look like: Link to the theme: Clearscreen Sharp for Windows7 by *K-Johnson on deviantART