How do I delete a protected file/change theme?

[Windows Central Question]

So, I recently installed a theme for Windows 7, but because of it, I suddenly can't change wallpapers. So, I deleted it. But what I didn't realise, was that there was an 'aero' theme there, and my laptop uses aero from that third-party theme, instead of the default aero theme. Now, this wouldn't be a problem, but that aero theme gives me classic windows borders and prevents me from putting up wallpapers. So, now I'm stuck with classic window borders and no wallpapers, with no way of changing it.
I can't delete it because it's a protected file and Windows won't let me do it (I tried safe mode, changing permissions, moving it away from the Themes folder, nothing worked).
Please help, I'm extremely desperate.

 

[spicypadthai]

Try a system restore. Windows Update or installing a program should automatically create a restore point so check if you have a recent one.