You need to flash the latest image on the Raspberry Pi 3 microSD card. You can download the image here.
Once downloaded, don’t forget to unzip the archive. The image should be 7.9 GB.
You can then use a software like Etcher (very easy to use, we recommend it) to flash the image into your microSD card.
We have modified the image to be a little bit smaller than most 8GB microSD card. If, however, your card is too small (like 7.85GB), please send us an email at firstname.lastname@example.org and we’ll give you a smaller image.