When working with projectile problems, the two most useful equations of motion are:
v = u + at and s = ut + \frac{1}{2}at^2 .
Remember that when the vertical component of velocity is positive, the particle is rising. At the instant this component is 0, the particle is at maximum height. When the vertical component of velocity is negative, the particle is falling.

For a projectile, the horizontal component of velocity is constant.