How to change some channel's info with javascript?

Are you sure the XHR the browser sends is a PUT?

If you’re using the CDN URL for the Twitch SDK (https://ttv-api.s3.amazonaws.com/twitch.min.js), it’s outdated and doesn’t support the verb option, so your request is being sent as a GET. Download the one on github.

You can also use _method: 'PUT' inside params. Here’s an example using both.