The BennVenn's ElCheapo SD has updatable MCU firmware. This is the internal code that the cart runs, not the menu loader. From time to time there may be new features added that will require this code to be updated, this is how it's done.
Firmware downloads will be available either here or on the BennVenn's Downloads page when new versions of the firmware have been released.
Step 1 - Put the ElCheapoSD into your Lynx, with the SD card inserted and turn the Lynx on. This is to make sure that the cart is working OK before you get started. Turn your Lynx off before the next step.
Step 2 - Flip your Lynx over and eject the SD card from the ElCheapoSD by pushing the SD card down into the cartridge. The SD card should click and eject, then you can pull it out. Leave the ElCheapoSD cartridge in the Lynx.
Step 3 - Download the latest firmware and copy it to the SD card. The firmware file will be called FIRMWARE.ben.
Step 4 - Insert the SD card into the ElCheapoSD and turn your Lynx on. The "INSERT GAME" screen will show for around 15 seconds. DO NOT TURN OFF YOUR LYNX while the "INSERT GAME" screen is showing, doing so will brick the ElCheapoSD and you'll be left with an unusable cartridge. While that screen is showing, the firmware is being updated from SD card to the cartridge.
The menu loader will boot up as normal after the firmware is updated. You can leave the firmware update file on the SD card, the firmware will not try to update to the same version multiple times.