Couchbase sync gateway UserAPI

I’m referring to the following API details to manage users in our couchbase server.

I have few questions to ask

How could I Edit a user through sync gateway. Like change the password, assign/unassign channels to user etc.

I see two api references to do the same task

POST /{db}/_user/
Create a new user
PUT /{db}/_user/{name}
Create a new user

Does first one intended to do the editing of a user.

How could I assign/unassign channels from users.