Question: how to change your name on twitch on ps4?
Answer: Login to Twitch.
Go to Your account settings.
Next to username, you'll see an Edit button, which looks like a pen. Click this. ... 
Enter your new username. Source: Windows Central.
If that username is available you'll see a green check mark.
Click Update.
Enter your Twitch password to verify, and you're good to go.