open App.lua
there is a line like
local window = Window:Create(self.title)
just edit to
local window = Window:Create(self.title, 0,0,x,y,Window.FullScreen)
x and y = screensize like FullHD = 1920, 1080
note that the resolution is related to your hardware
the scripteditor is a little bit hidden. I hope we get a Script Editor Button soon. To open the editor Run the game in debug mode or open a lua file in the filebrowser.