Before you try to change directions (turn) you must be able to Water Start and ride both ways. Level: basic
A twin-tip board is best for this and it allows you to change direction easily. Reasonable wind (say 20 knots) makes changing direction easier.
Simple direction change
The easiest way to change direction is to:
slow down at the end of a tack
bring your kite to 12 o'clock and stop
sink back into the water
do a Board Start and head back in the other direction.
Sliding turn (also referred to as "Sliding transition")
Once you are comfortable with a simple direction change, the next step is to master a sliding turn.
The steps are:
When riding edge upwind, take your kite towards 12 o'clock and push the bar out, all of which will slow you down.
Come to complete stop.
Fly the kite to 12 o'clock, shift your weight from your rear foot to the centre of the board, then pull down on the bar to stop yourself from sinking
Turn the kite in the opposite direction - the new direction you would like to ride in.
Lean back slightly and point your leading foot (which was your rear foot) in the new direction the kite is pointing and slightly downwind
Bend your back knee (which was your forward knee) slightly and transfer some weight to it.
Dive the kite in the new direction to get moving.
If the wind is strong you will not need to pull down on the bar much.
If the wind is light you will need to dive the kite more to generate power and fly it in a sine wave to keep moving in the new direction.
If you bring the kite to 12 o'clock too quickly you will get lifted out of the water - which could be your first jump!
If you bring the kite to 12 o'clock too slowly you will sink back into the water.
Don't move the kite before shifting your weight, and don't shift your weight before slowing down or stopping.
Make sure when you dive the kite that you bring it back up again - crashing it into the water is a common mistake while learning.
Judge your turn depending on the wind strength - try it slowly first. It is better to sink and Board start again than be over powered and be pulled over your toes off the board.