First - to drain the coolant, pull the bottom radiator hose off. On the side of both of the cylinders there is a 10 mm bolt, pull both of them. Pull the overflow tank off and dump it out. That wont get all of the coolant out but it will be good enough.
Second - put all of these things back together, take the radiator cap off and fill the radiator. Take the bottom radiator hose and squeeze it a few times then lift it up as high as you can without breaking the radiator. Repeat that step a few times to remove any air pockets. Fire it up and check the fluid to make sure it is full.
DO NOT START IT WITHOUT COOLANT!!
I cant remember how much you will need. I think only 1 jug should do it but dont mark my words.