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 din.
The following rules govern manoeuvres during a charge:
When a unit charges an enemy the player must endeavour to bring as many models from the charging unit 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. This is a very important rule, so be sure to get it right from the start!
During a charge a unit can wheel once. It can, and indeed must, wheel in order to maximise the number of charging models able to fight. Note that the unit does not have to wheel if this would mean that it cannot reach its enemy.
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.