Yes seated properly; I had an Integrated Intel HD Graphics 530 before and "no" I didn't do any uninstalling before I installed the new Radeon 580. I have since tried to go to "device Manager" and "disable" the device but after that I had all sorts of issues. So I am back to having two types of display adapters.
Ok, so hook the monitor to the motherboard(so you can see the bios), enter the bios and either set the 580 as the primary display adapter or disable the igpu. If you have no plans of running extra monitors using the igpu disabling it would be best as it will free up ram that was set aside to be vram for the igpu.