How the object accelerates?

Changes its energy of motion (kinetic energy), changes its momentum, changes its velocity.

Well, it is a quite simple assesment. When an object speeds up or slows down...I know you may be asking, "How does an object accelerate when it slows down?" because the velocity is not constant and...

it changes direction,it speeds up or slows down

All objects accelerate if the forces acting on them are not balanced.

Objects can accelerate by the change in their velocity. If their is a change, objects could speed up or decelerate.