Alter php.ini on localhost

I’m trying to run Worpress locally on my Windows 7 machine. I’ve installed WP using Microsoft Web Platform Installer and have successfully installed WP (and updated to v3.5.1) I have hit a problem with uploads as the php.ini file limits them to 2mb. I have opened the php.ini file in Notepad and changed the upload limit but when I try to save the edited file access is denied. I’ve tried removing the Read Only access in Windows Explorer but it has no effect.

What do I need to do to be able to save the amended php.ini file?

Thank you