FWIW it is currently only in the development branch of emulationstation.
Leave Emulationstation.
ssh with account pi to your pie:
Then you will have to do the "three chord":
./retropie_packages.sh emulationstation-dev sources #1 ./retropie_packages.sh emulationstation-dev build #2 ./retropie_packages.sh emulationstation-dev install #3If you want to adjust the delay do use this line before proceeding to step 2 and 3.
HTH