If he was an adult, there wouldn't be a problem - however with kittens it can get more complicated, as their immune system is not as developed. If at all possible, take him to the vet.
Watch his snot - if it's clear, he most likely doesn't have a bacterial infection. Make sure he is feeding and drinking well, even if it means you hand feed him. Turn on the hot water in the bathroom with the door close to get some steam going - keep him in there breathing the steam for a good 30 minutes. That should help to clean his airways. Try feeding him right after, as he will be able to smell the food better.
Get some L-Lysine supplements from the pharmacy (regular pharmacy), crunch one 250mg pill (or open a capsule), and mix it in his wet food. Do this in the morning and at night, so he gets 500mg.
Watch him very closely - if he develops a snot that is not clear, hurry him to the vet, even if you need to surrender him to the human society, as a bacterial infection in a kitten can be lethal.