When the ball collides with a solid or wall object, set its angle to
Ball.Angle + 160 + random(40)
That will change its direction by 160 to 200 degrees.
Next use an always event to move it by private variable "Speed"
X = Ball.X + Speed * Cos(Ball.Angle - 90)
Y = Ball.Y + Speed * Sin(Ball.Angle - 90)
Hope that helps!