Android moves pretty fast. It's important to know when, how and what to expect when you upgrade your device. Let's step through a recent upgrade from Froyo to Gingerbread on a Nexus One.
We are interested in a couple of areas here. First, we want to see what version of the OS we are currently running.

Checking the version
Notice that the current version on my phone is 2.2.2 and build FRG83G. Looking into that number a bit more it stands for Froyo and a variant of “GOOG”, with 83 in between the G’s. This is presumably a build iteration or number of the Google version of Android, as opposed to a version released by HTC, Motorola or others.
Let’s tap on “System updates” to see if there is anything awaiting us. Of course that’s a bit of a loaded question because we know there is an update waiting.

Manually checking for updates
Upgrading!
Regardless of how you arrived at this point (notification or looking for an update manually), go ahead and begin the download of the upgrade package.

Downloading the upgrade file
Once the download is complete the device must reboot for the upgrade to be applied. Note that we’ve got a few seconds to cancel the upgrade.

Reboot after download
Assuming we don’t cancel the upgrade, the phone reboots automatically.

Powering off
Please excuse the quality of the next two images as they were taken with low light via my son’s iPod touch — yes, Apple has creeped into my home….but we’ll keep the boy anyway. After all, he was kind enough to point out that the “P” in iPod is supposed to be upper case.
The first thing that takes place upon reboot is the downloaded upgrade file is unpacked.

Unpacking the upgrade file
Once unpacked, the file is processed and then the phone is restarted (again).

Processing the upgrade file
After the upgrade
Once the phone reboots it is obvious right away that something has changed because the look and feel of the OS has changed. Just for kicks, let’s again have a look at the Settings | About Phone information to check the version of the OS software. Also note the change in the appearance of the top status area — it is now lighter text on a darker background.

New version info
And checking for another update tells us that we are in fact already at the latest version.

System is up to date!
A (very) brief look @ Gingerbread
The new notification window has a slightly different look. Nothing here makes us say, “hmm where did the notifications window go”? It is simply a “different” look.

New notification look
And the dialer window has a new look also, among many other areas such as the keyboard and list animations, etc.

New dialer look
Please note that no real Androids were put in harms way or injured during this presentation. Nor were any iPod-toting youths.
If you have an Android device hopefully you will enjoy an upgrade soon as well.