I am a new user and I ran into this question too.
The UI is kind of strange. You have to change your password in qlik.com but not community.qlik.com
In qlik.com, as other has suggested, after you log in, at the top the left most drop-down menu say "Welcome, <yourname>", click on it or wait until the menu pulled up, select "My account" and go from there.
Hope this can help some other new users.