If you are unregistered in KT, just post something or answer, then there’s a box where you can change your name.
If you are registered in KT, log in, then click your profile to ‘Hello, <username>’. Go to ‘My Account’, then fill in the username box.
If you are registered or unregistered (coming soon) in KN, you have to ask KidzSearch to change your username.
I hoped this helps!
I will update this soon because a new update is coming to KN.