As competitive sailors know, wind direction is always fluctuating back and forth. The ability to play these wind shifts is one of the most critical principles of effective upwind sailing.
The same is even more critical for upwind kiteboarding because the upwind angles are relatively poor.
If you meet a windshift that causes you to alter course downwind, you have encountered a "header". Assuming that this isn't just caused by a lull, which will create an apparent header, this is the time to turn onto the opposite tack so that the windshift will assist your upwind angle instead of hindering it.
If the opposite happens, and you find your upwind angle suddenly improving due to a windshift, then you have encountered a "lift", so keep on going while it lasts. Note that a gust will also create an apparent lift, regardless of which tack you are on.
By choosing the appropriate tack for each windshift, you may easily reduce the time and distance travelled by a half or more to reach a point upwind.
Best regards, James