Draw your object on the Stage   Select the object, Go to Modify>         Convert to Symbol   Go to Modify>Break apart.
Select Frame 30 and Insert a Keyframe   In Frame 30, choose and delete the original object.   Draw another object in approximately the same position.  Make the shape a different color and shape and size.   Select the object and: Convert to Symbol & Break Apart   Return to the first deyframe. Go to the Property Inspector. In the Tween Pull Down Menu, select Shape Tween