Major Units have almost the same Information Window. However, there are some notable changes. In place of a Load value, you have a Combat Bonus. In place of a commodity chart you have a spell list.  In place of a Unit Carry, you have an Age indicator.  Also Major Units attack equally into all types of terrain.  There are a few different buttons as well.

Exp. lets you apply gained experience.  You gain experience either by engaging in victorious attacks or by growing up (see Offspring) In the dialog box that comes up, you can raise you combat strength, leadership ability and if you started with magic, your magic power. Each ability costs so many points to raise as shown in the dialog box

Sire  lets you sire an heir who will also be a hero.