on the motherboard go to the mb vendor web page and look at the chipset used for ethernet on the mb. it give you a model info of the chipset used. you then go to the vendor of the ethernet chip and look at the data sheet of your network chip.
most of the newer mb have 10/100/1000 chipset ethernet. 10g/100g/1000g. to get the higher speeds you need a router with 1000g ports and newer 5e/6 cat cables. before you go crazy use speedtest check the speed your getting now on wired and wireless. wireless use two radio bands...2.4g and the newer 5g. that not the speed they run at. speed of wireless depends on the chipset used in the router and on the dongle used and how close to the router your pc is.