How do I "upgrade" units?

[Xoon]

I have read several references to the ability to upgrade units, but neither the instructions nor the civolopedia have given much in the way of instruction or even what it means to "upgrade". Can anyone give me a little help here?

 

[Badluck]

first to upgrade your unit you need to have the ressource.
exemple *horse*

you also need to have a barrack in your citi where your trying to upgrade your unit.

you go in your citi and right click on it. you should see the option

Exemple: upgrade to pikeman.
there is also a *button* the make all your unit upgrade, the one that can but i don'T know what it is.

 

[Goat_Guy]

U could also upgrade the current unit by hitting "U" and upgrade ALL available units of the same type by hitting "Shift" + "u"