(This content is based on the "How do I update my Nseries device software?" N-Gage FAQ section, I just extended it a little.)

 

Firmware can be updated via PC by following these steps:
 
[0.]
Check if you have the latest version of Nokia PC Suite (v7.0.8.2 or later).
[1.]
Backup your phone memory to your PC using PC Suite (needed to preserve your Game progress!)
[2.]
Copy your files (music, videos, documents, images etc) from the Nokia memory card or hard drive (if available) to your PC(use of USB mass storage recommended).
[3.] Copy your music, images and original SISX, Java, etc. installation files for your applications, themes, etc. from your Nokia memory card or hard drive (if availabl) to your PC. (Do not simply copy over installed application's directories/files.)
[4.]
Format memory card or hard drive (if available) by selecting Tools > Memory > Options > Format mem.card > Format memory Card
[5.]
Upgrade your phone's firmware with with Nokia Software Updater (NSU)
[6.]
After the device has completely started up again, reset your device memory by selecting Menu > Tools > Settings > Phone > General > Orig. Phone Settings and enter 12345.
[7.]
Restore your phone memory from your PC using PC Suite by selecting Backup from the PC Suite menu and then selecting Restore.
[8.]
Copy back your hard drive or memory card contents from your memory card or PC to your clean memory card or hard drive (if available).
[9.]
Reinstall all your N-Gage games one-by-one! That must be started on the PC (Bounce.eng.exe, Reset_Generation.eng.exe, ...)
 
Ta-da! All your game progress is preserved!

 

I tested this today on my Nokia N95-1 with upgrading firmware from the old v21.0.016 version to v30.0.015!
Everything went good.
 
(In the original FAQ the last step is missing. Don't know why, because it is very important!)

The [9.] step detailed:

 

[9/a.]

Start the appropriate game installer EXE file on PC (with active PC Suite connection) and process all steps!

[9/b.]

Start the N-Gage application on your phone and wait for the installer, it will make an initialization

[9/c.]

Select the appropriate game icon and start the game install and process all steps!

(The game location should be the same as it was in the old firmware.)

[9/d.]

Start the game!

 

 

I am not entirely sure! But the original FAQ also contains this step:

"

How do I update my Nseries device software?

---

"

But it is possible, that you can omit that step!

In any case I always format my microSD card before a firmware

upgrade (after making a backup of it of course)!

That spares me a lot of trouble!

The main counter-argument of doing this is the ultra slow copy time.

To copy back all data to my 8GB microSD card, I must wait about 1,5-2 hours! :-(

But a firmware upgrade is relatively rare.