If you currently have CircuitPython installed on your UM board, first download the .UF2 file of the CircuitPython version you would like to install from https://circuitpython.org/downloads?q=unexpected+maker
Then put your board into UF2 Bootloader mode by following these steps.
Once you see the UF2 BOOT Volume, copy the donwloaded .UF2 file to your UF2 BOOT Volume.
Once copied, your board should automatically re-start and boot into the updated version of CircuitPython.