Repo for image updates
You just need to connect by ssh with putty or similar and execute the following command:
For Freeplay with cm3:
wget -O- https://raw.githubusercontent.com/julenvitoria/FreeplayGBA/master/cm3/install.sh | bash
For Freeplay with zero:
wget -O- https://raw.githubusercontent.com/julenvitoria/FreeplayGBA/master/zero/install.sh | bash
NOTE: IT'S NECCESARY THAT YOUR GBA HAS INTERNET CONNECTION