Last week I installed a desktop and thought I should install Ubuntu 16.04 Xenial Xerus right away. That would prevent a later upgrade. As I understand in these last weeks nothing really changes, it's mostly testing.
Now I would like to know if I need to change the channel from RC (release) to stable, or if this happens automatically? How can I check this?
No, you don't need to change anything.
If you want you can check the package sources in the file
/etc/apt/sources.list
:All lines that don't start with a
#
should have something withxenial
in the third field (after the URL), for exampleor