With the spell resolved, the casting player can now have the same or another of his Wizards attempt to cast another spell.
Wizards can cast spells in any order, and a player is free to switch between Wizards at any time provided that he does not do so until the casting of the current spell has been resolved.
Remember that, unless specified otherwise, each Wizard can cast each spell only once per turn. When the casting player has finished all his casting and dispelling attempts, either because he has run out of power dice or has no remaining or useful spells to cast (or if all his Wizards have had their concentration broken by failing to cast a spell) the Magic phase ends, and the Shooting phase begins.