Should be a straight forward operation...
put the card in the PCIe x16 slot,
power the card's 6/8 pin header if so equipped,
move the monitor's cable to the new card,
turn on the PC (you should get a display),
boot to Win,
install the card's gfx driver.
But be sure you have enough PSU for the card you choose. A gfx card can be the most power hungry device in your PC.