I recently bought Aspire V5-572 Laptop. Actually it supports windows-8 only. But Sales Executive changed bios version and installed windows-7. now, am trying to reduce brightness. but it won't happened. i was not able to find any graphic drives for this.
My guess is that you are missing the utility to use keybd shortcuts (Fn+F4 for brightness up on my laptop) from your installation. If the brightness can be adjusted from the windows control panel power options then that sounds like what you need. I've no idea if you will find one that works.