How can only the change in direction can be called acceleration? Why does the change in only the direction leads to acceleration of a body. I mean acceleration of body implies that it is moving fast or getting slow with respect to its initial speed.
But i dont think that change in direction affects any of it?
 A: It's not just about total speed, it's about the speed in each direction -- i.e. the velocity vector. 
If I'm driving east at 60kph, and I turn left using a turn of some radius, but maintain the same velocity to end up going north at 60kph, my direction changed, but my total velocity remained constant. But my velocity in the eastward direction decreased from 60kph to 0kph, which means there was an acceleration in the westward direction. My velocity in the northward direction increased from 0kph to 60kph, which means there was an acceleration in the northward direction. Around such a curve, the acceleration is a vector pointing inward. 
A: Acceleration is defined as the change of the velocity vector. It is not that the latter leads to the first. A change in direction requires a force just like a change in magnitude, i.e. the moon orbiting around earth.
A: To make a body go faster or slower you have to exert a force on it. 
Try tying a rock on a string and swinging it around in a circle. You can't do it without pulling on the string, even if the speed is constant. If you let go, the rock flies off in a straight line. 
