Yes, we change also the conjugation. For example "tu sei", "voi siete", "lei è" (I used the verb "to be"). The history behind the usage of "voi" and "lei" in italian is very long and complicated and there are also regional differences, for example "voi" is still used in some regions of the South (for example in Naples). But "voi" was imposed by the Fascist government in the italian society, and later it was replaced by the feminine third person "lei" (it is feminine also if you are talking to a man... This is due to the origins of its usage...) :-D Insted the normal masculine third person is "lui", but only the feminine "lei" is used as the "formal you"