Blower

It depends on lots of stuff:

If it is an axial fan, the air will move in the opposite direction.
--If the blades are curved, the efficiency will decrease.
--If the blades are flat, the efficiency will remain nearly the same.

If it is a centrifugal (squirrel-cage) fan, the air will move the same direction, but:
--If the blades are radial, there will be a minor decrease of efficiency, depending on discharge direction.
--If the blades are forward curved, the efficiency will decrease.
--If the blades are backward curved, it depends on the angle.
- - -If very shallow, the flow might even reverse (not sure).
- - -If steep, the flow may even increase and perhaps overload the motor.

Some less common geometries would have yet further variations.

"if we reverse the direction of motion of the fan inside a blower what would happen???"

That would really suck, wouldn't it?

Oh, and I think Tornado pretty well has it covered.