microStudio uses the full resolution available on the user's screen. If you want to make your game look 256x144, you will just have to scale your sprites accordingly. The coordinate system automatically sets the total view height to 200 "units" when in landscape mode, thus here is how you could draw an 8x8 sprite:
screen.drawSprite( "my8x8sprite", x, y , 8/144*200 )
Oh and I almost forgot, you could also just scale the screen once and then use your own coordinates system all along:
screen.setScale( 200/144, 200/144 )
// you can then use
screen.drawSprite( "my8x8sprite", x, y , 8, 8 )
As 256x144 is a 16:9 ratio, you may also want to select "force ratio: 16:9" in your project settings.