How do I upgrade any unit?

[Transcend]

Can someone please tell me? Thanks!

[FeathersMcGraw]

Move the unit into a city that has a barracks. If the unit is upgradeable, an upgrade button will appear over the unit action icons at the bottom middle of the screen (I think the keyboard shortcut is "u"). You'll get a dialog asking you if you want to pay for the upgrade.

You can also upgrade units in the city screen by right-clicking on a unit in the garrison and selecting upgrade. You can also do this from the military advisor page.

What I'd like to know is if there's any way to upgrade a group of units at once (like all the units in a city or all of the units of a particular type). Even going through the military advisor page selecting the upgrade menu option is a bit on the tedious side, particularly given how large some of my standing armies get.

[Yossarian]

Shift-U

[Warmaker]

I also believe that when upgrading you need the appropriate resources to upgrade the unit to. For instance, if you only had one town with access to iron for the rest of your empire and all the sudden you lose it, it means that you shouldn't have access to all the units that require iron for making (legions, samurai, etc.)

[Spagina]

My question is, can you upgrade units that are on separate continents? I've noticed on many of my island hopping games that I can upgrade my units on my capitol continent, but on my colony islands I'm having an extremely hard time upgrading them.

[Transcend]

Anyone has an idea how much the upgrade usually costs?

[ixnay]

Its twice the difference of the cost between the upgraded unit and the obsolete unit.

[Blaupanzer]

Originally posted by Spagina
My question is, can you upgrade units that are on separate continents? I've noticed on many of my island hopping games that I can upgrade my units on my capitol continent, but on my colony islands I'm having an extremely hard time upgrading them.

You'll need harbors on your main continent and the island city in question. You also need the technologies that allow trade across seas and across oceans if either intervene between the island and the mainland. Otherwise the island needs independent access to the strategic resource(s) required.