★★ You can vote one time per week for the Champion Song (the show is on Wednesday nights now).
You must have an account on melon (log in with either a melon ID or a One ID), but you do not need to have a "full" account [one that you can use to purchase & stream music - this requires a Korean ID number].
>> My tutorial to sign up for melon

① To vote for the "Champion Song," you must access melon at this link:
http://www.melon.com/cds/musicstory/ontv/web/ontv_list.htm?ckey=SCHM

You will see a list of episodes.
Click on any of the SHOW CHAMPION titles as shown:

② You will be redirected to a voting page.
(You can also win tickets to the show if you vote)
If you click on the purple [챔피언 송 투표하기] button, you will get a pop-up window with a list of options to vote for.

③ Scroll down to Teen Top's song and click on the button that says 투표하기 (vote).
You will be prompted here to log in if you haven't already.
You can vote once per week.