Click Start Orb. In search type cmd and hit Enter.
In the command window that popped up type
echo %ProgramFiles% and hit Enter
It should tell you the current setting as in
You can take a look at this: Change Default Installation Directory In Windows 7 & Vista
But before messing with your Registry make a Restore Point and/or use ERUNT
to back it up.
I just did search and took a look at the registry settings in the link. I don't know if it works. Back things up before messing around with it.