To install or update Screenly on your Raspberry Pi 3/B/B+ or Box 0 player you will need: a microSD card, a microSD card reader, and the free program Etcher installed on your computer.
You can download Etcher here.
Another option for a flashing tool is the Raspberry Pi Imager linked here.
Where to get an SD card
If you do not have an SD card reader you can buy one here, or any other retail location.
Steps for flashing out Screenly to an SD card
1. Download and Install Etcher. (Note: Ensure you are on a minimum version of 1.5.116, or the latest version).
2. Copy the link below for your hardware.
3. Plug your SD card into the SD card reader and the reader into the computer if it isn't already. In Windows, you might see a pop-up asking you if you want to format the SD card. You should format the SD card in the FAT32 format.
4. On your computer open Etcher.
5. Etcher will ask if you want to flash from a file or a URL, select "Flash from URL". Then, paste in the relevant URL that you copied in Step Two. Next, click "Select target" and choose your microSD card. To start the flash, click "Flash!". The flashing process may take a few minutes.
6. Once Etcher is done flashing the card, right-click on the microSD card drive and select "Eject". The drive will then be safe to remove.
7. Remove your SD card and plug it into the tiny slot on the bottom side of your Raspberry Pi motherboard.
8. You're done! Put your player back together, plug it in and continue with the setup.
Frequently asked questions on flashing out Screenly to an SD card
Q: When I view the SD card contents on my computer it says that it has a much smaller capacity than before, it went from 16 GB to 31 MB! What's up?
A: The storage space is still there, we've just formatted it in a way that it will not show up correctly on Windows or Mac OS. This is normal, don't worry about it.
Q: When I insert the SD card into my computer it says that it is locked or read only and I can't format it, what do I do?
A: SD Card adapters have a physical switch on them that locks the card into read only mode. Flipping the switch down should unlock it. See this KB article from Sandisk for pictures.