You will quickly outgrow your little starter base. You'll run out of storage for your resources, and you'll want to start building all the cool stuff in the game that isn't unlocked until you've built and/or upgraded specific buildings. Upgrading your buildings is a key element of your War Commander strategy, as it's those upgrades that will allow you to grow into a force to be reckoned with!
In much the same way as it can't build more than one building at a time, your Worker drone cannot upgrade more than one building at a time, so you'll want to plan your upgrades in advance for maximum effectiveness. (If you're uncertain what the best upgrade strategy might be, don't be afraid to connect with the War Commander player community via the forums and Discord!)
To upgrade any building, just click on it and look for the "Upgrade" button.
For this example, we chose an Oil Storage building.
When you click that Upgrade button, it will bring up a window like this one:
There's a lot of information to consider in this window, so let's break it down a little. First, we see that at the top of the screen, the window gives us a sense of what we'll get from the upgrade. Since this is an Oil Storage building, we see that the upgrade will increase the building's capacity to store oil.
We can also see what the upgrade's resource cost will be. Those two symbols on the top row there are for Metal and Oil, as you'll recall; the one on the bottom left is Thorium. If a particular resource type is not required for an upgrade, it appears greyed out here.
Finally, we can see how long the upgrade is going to take.
To get your upgrade started, just click the "Use Resources" button. It's that simple!
If the upgrade is going to take a while and you want to finish it faster, you can either use the "Instant" button to use gold to complete the upgrade immediately, or you can click on the building in mid-upgrade and use gold to complete any remaining progress.
When you upgrade a building, you are upgrading that specific building. You are not upgrading all buildings of that building type. In other words, upgrading one Power Plant will not upgrade your other Power Plants. While combat units are upgraded by unit type, buildings upgrade individually.
As you upgrade buildings, you'll find that they change appearance. By which we mean they just keep getting cooler. Just wait...you'll see.