A charging unit cannot turn or change formation. This is because the troops are running or galloping once the charge has begun, and are unable to execute delicate manoeuvres even if they were able to hear the orders of their leaders above the shouting and din.
When a unit charges an enemy the player must endeavour to bring as many models into combat as possible. This can sometimes be achieved by moving the chargers straight forward, but often it will be necessary to wheel slightly to face the enemy.
A unit can wheel once at the start of the charge in order to bring as many models to face the enemy as it can. If the chargers would not hit their target were they to move straight forward, then they must wheel to face their enemy, and must endeavour to bring as many models as possible into combat.
If chargers need to wheel towards their target, execute the wheel as already described measuring the distance wheeled as you normally would. This distance counts as part of the total distance charged. For example, if a unit can charge 12" it might wheel 4" to bring models to face the enemy and then move up to 8" towards them.
Once a unit has completed any required wheel it is moved straight forward towards the enemy and stops as soon as the two units touch.