A unit of troops can change the direction in which it is facing and rearrange its formation all at once by means of a manoeuvre called reforming. The leader issues the order to adopt a new formation and the troops assume their new positions.
A unit of troops can reform during its movement phase as long as it is not in close combat, and is not subject to some compulsory moves. The player declares that the unit is reforming and regroups it into a new formation. Keeping the centre point of the unit the same, arrange the unit into a new formation of as many ranks as you please, facing whichever direction you wish, so long as none of the models in the unit move more than twice their Movement rate (ie, Men with Move 4 can move up to 8). Characters, champions, standard bearers and musicians must still be placed in the front rank of the unit as normal.
A unit that reforms cannot move that turn because it takes the entire movement phase to reform. Also, reforming troops cannot shoot with missile weapons that turn because they are too busy assuming their new formation. Other actions, such as Wizards casting spells, are still allowed.