AnImAtIoNs: Have a look at the platform-tutorials.
CHanGE direction of the bullet: you can use a instance-variable direction. This variable should changes the walue when you press left or right. At the shooting: Change the angle of the bullet depending on "left" or "right". quick and dirty example with your file
—: Please use dropbox for your files.
— of your sprites: sprite1, sprite2, sprite3 are useless and unreadable names in porgrammlogic. Give them names that describe their task eg: Player, Bullet, ...