To fully update your Pi’s software, or refresh it if you think it’s not working correctly, you can flash our SD card image onto the microSD card in your Pi.
To update the SD card, you’ll need to download our image,
pi-image.img.xz. The flashing procedure is identical to flashing other Raspberry Pi images.
We recommend using etcher, as it’s simple to use, and available on Windows, macOS and Linux. If you’re familiar with Raspberry Pi’s and have flashed images before with a different tool, that will also work.
If you choose to use a tool other than Etcher, you may need to extract the
pi-image.img. There are many tools available for this, e.g. 7-zip.
pi-image.img.xzfile you downloaded
The Raspberry Pi Foundation also have a good tutorial for all platforms on their website.