To chose and / or sort your channels, press "Edit" (1.)
You can find channels by scrolling up and down (2.), or by searching for them (3.).
To select or deselect a channel, press it to toggle the "check" mark (4.).
If you wish to sort the channels, press "Sort" (5.) or press "Done" if you are (6.). This will take you back to the Now screen.
To sort the channels, press and hold to the right (6.) and drag it to the desired location.
Press "Done" to return to the Now screen.