Is it possible to upgrade the version of Android OS?

It all depends on what your phone is. Nexus One gets a firmware swissie in the shortest possible time directly from Google. HTC Desire, as his brother also gets them in a short time. With other devices more difficult, craftsmen harder to make an updated build, but they, nevertheless, there is. Most "multidevice" — CyanogenMOD:
1. Nexus One
2. HTC Aria
3. HTC Dream / HTC Magic
4. Motorola Droid
5. HTC Desire
6. HTC Evo
7. HTC Slide
8. HTC Hero CDMA
9. HTC Hero GSM
10. Samsung Galaxy S
11. HTC Incredible
12. HTC Legend
It is collected from source posted by Google and the manufacturers. Often not working things like camera, FM radio, etc., because these things strongly tied to specific glands, but the rest of the firmware is quite stable.

My cell phone HTC Desire equipped with some version of Android. The manufacturer first released the update, and then for some time hid it from the public, but through the special key combinations allow us to enter the mode that allows you to apply the upgrade (in advance prudently pumped) directly from flashabou card (and not through the air from a distant website). This mode is intended for employees of service centers.

Just download and compile will not work — need the drivers for the hardware. As a rule, if the manufacturer delays the release firmware with the new Android, you can install custom firmware (full on 4pda).

You can try to put left firmware, but if the phone is locked then nothing happens.

I advise you to look at forum.xda-developers.comif somewhere there is a firmware version of Android for your smartphone — most likely on this forum it will be with instructions and a description.