In spite of some false preconceptions, you can ride your Kickbike nicely also uphill. You need to master the technique, though, in order to take advantage of the light 9 kg weight compared to an ordinary bike.
When the road starts to ascend, the Kickbike tends to slow down noticeably between the kicks. However, don't slow down consciously. Instead, alter your technique. Increase frequency. Take shorter kicks. Change your pendulum-like kick to a rotating one. When you keep your kicking knee slightly bent you can bring the leg quickly back to the front for a new kick. In the kicking phase, however, try keep your legs straight avoiding excess vertical movement. If you wish to increase your frequency further, you need to learn the jump-change of the leg. Jump immediately after you have kicked and are bringing your kicking foot to the front. A low, almost inconspicuous jump does not waste too much energy. If the hill is too steep for your fitness or skill, don't be discouraged. It is extremely easy to move into running or walking. For a beginner this is often the most convenient alternative.