Originally Posted by
Biffoniacus_Furiou
"As a full-round action, the familiar can change its form to that of any creature that the wizard could normally have as a familiar (see page 52 of the Player’s Handbook)." It can't change into a Winter Wolf unless you have the feat Improved Familiar, a caster level of 7th, a +7 BAB, and are within one step of a Neutral Evil alignment.