how do i find port?

i need to know how to find the port that ragnarok online uses on my computer, im trying to open up more ports for it on my router so that i can play the game without too much lagg... my roomate uses 2 comps to download who knows what and its lagging my net up.  thank you in advance

Configure your modem`s router to port forward ports 20, 21, 80, 443, 4500, and 6900

2 seconds in google