One way would be by comparing touch x and y position.
When touch begins store touch x and y in variables. Then if touch x > stored x + desired distance that means player swiped his finger to the right by that distance.
Touch x < stored x - desired distance = right.
Touch y < stored y - desired distance = up.
Of course, that could mean player could swipe on whole screen for such effect, if you want him to swipe only on designated joystick object you should add event above "is touching object"