upgrade items??!?!

[Loki Mundane]

I have read many a times about how people have "up'ed" their items but have searched and searched and have not been able to find out how this is done.
I am assuming it is done with the item, the cube, and some other items.
Could someone explain this to me or point me in the right direction?
thank you

[frish]

here you go (http://www.battle.net/diablo2exp/items/cube.shtml)

the upgrading recipes are almost at the bottom