According to the third law of motion every body exerts action and the other shows the reaction.But the action and the reaction force and reaction force exerted on both the object is same then why the object changes it's position when it is also exerting the same force on that object?
Yes, this can happen...
The magnitude of the force exerted by one body on another could change in some situations, like when one is moving with respect to another or its position changes. So, in this case as the action force varies the reaction force will vary with it as the two occur in pairs.