Go to Run.
Type: regedit
Backup your registry:
Highlight My Computer
Select File>Export
Name it backupreg
Now navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion
On the right side, find the string called ProgramFilesDir and modify it to the desired
path.
If you run into problems installing Windows update or any programs in the future, just make sure to change it back to the default setting. It's a better idea to just change the installation path manually with the program you are installing. I don't see any reason why to tweak the registry unless you're always installing programs constantly.