There are 3 steps to install Quill OS on your eReader: download, flash and setup. To download Quill OS, visit the Downloads page.
To flash Quill OS to your eReader, take out the internal MicroSD card by taking off the back cover (be careful!). It must have at least 4 gigabytes of capacity. Insert the card into your computer.
On Windows, use balenaEtcher to flash the Quill OS image file to the MicroSD card.
On Linux and MacOS, balenaEtcher is the easiest option for command-line-reluctant users. Alternatively, you can also open a terminal and check the device node of the eReader's MicroSD card with fdisk -l. Then, write the image to the SD card, like this:
xzcat inkbox.xz | dd of=/dev/mmcblk0
To boot Quill OS, eject the MicroSD card from your computer and insert it in the Kobo's slot. Put the back cover on and power it on. It might take a while to boot, so be patient. Setting Quill OS up is easy; just follow the instructions on the screen.
Once that is done, it is strongly recommended to update to the latest version.