Personally I think it should be in a separate menu a la the crafting menu.
For example this would be the Inventory menu :
And this would be the Armor menu :
How it would work is in the inventory all armor would be sorted so armor is always behind blocks/items/others, armor would also be sorted so that all leather armor would be grouped, all diamond armor would be grouped, etc.
In the armor section it would be the same except that they would also be sorted so that Diamond armor was on the top, Iron armor in the next inventory slot Gold armor in the inventory slot after that, then Leather armor after that.
It would not only keep everything clear and easy to keep track of it would also make it quicker and more efficient.
Selecting Armor (to wear from the Armor section) would be as simple as one tap on the piece of armor and it would immediately equip it.
Also yeah I know I'm horrible at photoshop but this just pretty much illustrates my view of the "perfect" armor system.
Also why do you want to change the Main Menu?
All that'll do is increase the file size.