Download the newest microSD card image from here:
Download any SD-card burning software.
To access microSD card from your Rover, open the main electronics box (4x cross-headed screws) and extract the card from white-tape SD-slot extension slot located on top of the electronics.
Looking at the inside of the electronics box cover, you'll see a microSD-to-SD card adapter secured in a slot. Take it.
Put the microSD card in the adapter and then connect it to your computer. Open Etcher and point it to your new SD card image location via 'select image' (.img file). Then your card should be pre-selected in 'select drive' option. And 'Flash!'.
After the flashing completes, disconnect the card and put it back into the Rover.
You can fix this: