Cannot Upgrade graphics card in Bootcamp for AMD Radeon HD 5750

Game Players using X86 systems and Windows to play modern games must choose CLEAN type driver updates to avoid leaving behind items likely to cause conflicts, as has happened to you.  To unravel things now, you must first remove the current driver, then use a utility similar to Ccleaner and flush out any detritus remaining, THEN you can install current video drivers. 

I'm used to only updating the drivers via new bootcamp drivers from apple.com.

Q: Have you first checked to ensure you have done that step, prior to trying the AMD download if required?

• Go to [Apple] Boot Camp Support Software 5.1.5621, which applies to iMac (27-inch, Mid 2010), and follow the instructions there (exactly as per that article).

• Run DXDiag in Windows after performing the above step, check and note what Graphics driver you now have

• Only if necessary (if the APple Update did not include v13.12 or better), necessary, go to [AMD] Apple Boot Camp Software Graphics Drivers and grab the 169MB v13.25 drivers. Perform a clean install of those drivers if you can!

Hope this helps!

Apple/AMD only releases a new graphics driver for Boot Camp once or twice a year.

If you want to use the most current driver under Boot Camp go to https://www.mxdriver.com. They are pretty fast in adjusting the current AMD drivers for Win 64 Bit to run on your Mac.