why the flaps operation in the aircraft is always in the downward side ,why cant we use in upward side?

The main purpose of flaps is for when approaching to land , Extending the flaps (downward)increases the wing camber and the angle of attack of the wing. This increases wing lift and induced drag,(because they extend and increase the overall wing area) which enables the pilot to increase the angle of descent without increasing the airspeed. . The use of flaps also decrease the stall speed allowing the airplane to land and take off at a slower speed(decreasing the roll on the runway)because of the added lift.

If they were deployed upward, you would have the opposite, undesirable effect

Some airplanes actually do this. They are called flaperons, which is flaps which acts as ailerons aswell. The flap moves UP to decrease lift and DOWN to increase lift, just like an aileron. Some heavy aircraft actually employ 'aileron droop' systems, which is an aileron that actually extends like a flap.

If you want to spoil the lift you have to spoil the airflow on the upper surface of the wing, which is the main contributer to creating lift, so spoilers are the norm. On modern airliners such as 737, 757, A320 etc, they will employ spoilers to assist in rolling the aircraft. The upgoing wing creates more lift whereas the downgoing wing needs to have a reduced lift so the aircraft can roll, therefore the downgoing wing will extend the spoiler to spoil the airflow, and, in doing so, assists the roll, which is mainly the ailerons job.

On the upward side they are called speed brakes or spoilers and only add drag and spoil lift. Downward can also increase lift by deflection of the air downward.

It's perfectly possible to do as you suggest. Aircraft designers can put control surfaces in all sorts of positions, for all sorts of reasons.

However, by definition, flaps are control surfaces that increase lift, and that normally requires that the control surface move downwards, not upwards. If it moves upwards, it's not a flap.

They do act as explained in the previous answers.

Pretty limited Huh, flaps that will only operate downward direction....Lol

it probably won't be long and aircraft will have a integrated control surface on the wings like some fighters. Think of it like a common control surface all along the trailing edge of the wing that will both modulate like an aileron and droop like a flap.

What you suggest would produce the opposite effects. Downward allows the plane to fly slower because it generates both lift and drag. The upward motion would kill lift and produce drag. A fatal combo during landing and take-off. Most planes now have both available using two different pieces of equipment. Flaps to aid landing and when the weight of the plane is on the gear spoilers extend to kill lift and increase drag.

You could but it's not done because most airplanes need both at the same time so they need two different devices instead of a single combination device. They need flaps to reduce the landing speed and spoilers to kill lift as soon as the wheels touch down for more effective braking and steering.

As Mr AUDU stated, if the flaps moved upwards, the nose of the plane would be in the ground.

Flaps are extended on flap tracks, very strong ribs attached to the wings, that make up part of the trailing edge. There is no way to move them in both directions.

Because the aircraft needs lift to take-off/land at a "lower speed." While a spoiler decrease lift.