Editing apple 2 games sprites

The Apple II has no hardware support for sprites. The CPU needs to manually flip memory bits to draw anything on the screen. Hence, there is no standard format or standard way of drawing a moving graphics object. There may be programs which have a copy of an object's pixels somewhere in memory (similar to a sprite) and which manually copy it to the graphics memory area. Other programs may just generate objects on the screen "programmatically". But there is no generic way, like for the C64, how such graphic objects would be stored in memory.

Well...

Some programs did use a standard called "shapes."  The most famous example was Oregon Trail.  Though done partially in machine language, the drawing of a shape was still slow enough that you could sort of see its action with your naked eye. It was not great for animation reasons. Theoretically if you dug into the program you could substitute a different shape in, for say example say a stage coach for the wagon that is shown in the program.

Some people have hacked existing programs and replaced the patterns of a drawn object. The most famous example of this is the game originally called Castle Wolfenstein, it was renamed Castle Smurfenstein. Smurfs were substituted in for Nazi guards.

There were a few add in cards that had hardware capable of sprites. But they were expensive and now fairly rare. And only a handful of software supported them. 

There are many ways to do this.

1.  Hit reset, and if the game doesn't clear the screen on reset, you can save the screen buffer.

2.  Disassemble the machine code.  Find out how the bitmaps are rendered on the screen and extract the images from the data.