Replace explorer.exe with another?

Hey

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

Worked now thanks, however i did like this, cause apparently i didn't really take ownership of the both files, so i had to take overship of the Orgininal explorer.exe by chaning the owner to administrator, and then change the rights of the file for administrator. and then i could rename the file like you mentioned to something else and then replace it with the new one and then it worked :)

So i took owner ship of the orginal file and im made my self administer but when i click yes i would like to change the name a window pops up says i cant and dont have permission please help im running windows 7 64