[eLezer]

Thanks for your answer.

If needed, here the instructions I used:

Putting the ePub on your Kobo eReader

1 Plug the USB cable into the Kobo and plug the end that you normally put into the adapter into your computer;
2 On your Kobo, press ‘Connect’;
3 Your Windows computer will then give you a message that a device is connected. From the message, go to the corresponding Kobo folder. You can also go to the Kobo device that has now appeared via Windows Explorer, which can be found in the left bar under ‘KOBOeReader’;
4 Open the folder containing the ePub books that you want to transfer. Drag these files to the KOBOeReader folder;
5 Once the ebooks have been transferred, right-click on the Kobo in the left bar of the Explorer window and click ‘Eject’. Now wait for a message that says that the Kobo can be safely removed. This prevents files from becoming corrupt;
6 Remove the cable from your computer and from your Kobo. Enjoy reading the transferred ePub(s)!

I would say, simple instructions.
Calibre is on my laptop. I'm just not (yet) familiar with that programm.

The new transfered books are not DRM protected. The orthers probably are, because I bought/hired them.