The Desaturate submenu contains operations that turn an image into a Grayscale representation, using different methods.
Sección 8.29, “Color a gris”
Sección 8.30, “Desaturar”
Sección 8.24, “Mezclador mono”
Sección 8.32, “Sepia”
You can access this command from the main menu through Colors → Desaturate.