IM SORRY THE WEB AND PHOTOSHOP IS IN POLISH LANGUAGE.

You need create a 26,667 x 2,111 inch file.

Now you can modify the banner and save it.

If you save it you need go to web and click your avatar, when you done, click the settings (ustawienia).

Now upload the banner.

Choose the file.

If you do this, click the update button (aktualizuj).

The final result:

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