You don't really "replace" the APU, you install a Graphics card and (just to be sure) disable the onboard Graphics processor in the bios of the APU.
If in BIOS Settings you have not changed anything to do with your Default Display Adapter as soon as BIOS senses you have a GPU card installed it will automatically make your GPU card the Default Display Adapter for your PC and make the IGPU secondary.
The only affect you will have installing a GPU card is if there is any bottle-necking, if any at all, from either the CPU or GPU card.
Make sure if you are going to install a GPU Card that you have a sufficient minimum PSU wattage to run the GPU Card in your PC.
You don't really "replace" the APU, you install a Graphics card and (just to be sure) disable the onboard Graphics processor in the bios of the APU.
If in BIOS Settings you have not changed anything to do with your Default Display Adapter as soon as BIOS senses you have a GPU card installed it will automatically make your GPU card the Default Display Adapter for your PC and make the IGPU secondary.
The only affect you will have installing a GPU card is if there is any bottle-necking, if any at all, from either the CPU or GPU card.
Make sure if you are going to install a GPU Card that you have a sufficient minimum PSU wattage to run the GPU Card in your PC.