How would you "add on" to my integrated video card?

I recently got a new PC, and when the time comes i want to replace this graphics card

http://www.geforce.com/Hardware/GPUs/geforce-gt-530-oem

can anybody explain if i would be able to install high end graphics card around 4 years from now?

I have a dell XP8300.|||Yes, it has a PCI-E slot on the motherboard. When you put an add on card in it disables the onboard video and uses the card in the PCI-E slot