1. Remove old ROMs
2. Insert new ROMs
That's basically it. If you've never replaced a chip before, a good way to get them out of the socket is to insert a flathead screwdriver between the chip and the socket (not the socket and the motherboard!) and gently turn it left and right. That will slowly lever the chip out. You'll probably have to do this near each corner of each chip.
Other thing to keep in mind is that it *does* matter which chip goes in which socket. The instructions you got with your new ROMs should tell you. If not, some motherboard photos around the web probably will.
Finally, I believe there are more pins in the socket than there are pins on the chip. Make a note of how the old ROMs are positioned in the socket before removing them and insert the new ROMs the same way. Again, online motherboard photos can help with this, too.