Try getting the latest driver from AMD that includes the Catalyst Control Center, then you should be able to adjust the scaling.
I tried using Chrome for this post and it says my image uploaded ok, but if you can't see it, the only tab that shows a monitor is listed as HydraVision but I looked in each option under that tab and there is no scaling. When I open CCC, a message saying the video driver is not functioning and is being "unloaded" or something like that. After some searching today I am wondering if the driver that downloaded through the Windows update is not too specific for my particular setup. There are drivers listed if I try to pick my own (4 that specifically say Radeon 5470 and the most recent one says Radeon 5000 series). It is the last one that switched my screen to the black box situation. I guess my video card is like those for a laptop? I went back to AMD's website to download the driver for that "type" of video card but that one did not install successfully either. I have sent them a ticket request but not sure how long they will take to respond. I guess I could revert to my old driver and see if the scaling option is in the CCC (if it will open) but never needed to worry about it as my monitor was used entirely with that one.