Be very careful, when you are upgrading the code.
There are two codes to be upgraded
1) PROM code ( 3225prom.b29)
2) RUNtime code (3225run.b55)

You can ONLY upgrade ONE code at ONE time.
So, you have to do it one by one (basically similar process TWICE)

When upgrading the Runtime code, make sure you modify your 3225G.cfg file to be:
#Code_type=PROM
#Image_file="c:\DES-3225G\3225prom.b29"

Code_type=RUNTIME
Image_file="c:\DES-3225G\3225run.b55"

When upgrading the PROM code, make sure you modify your cfg.txt file to be:
Code_type=PROM
Image_file="c:\DES-3225G\3225prom.b29"

#Code_type=RUNTIME
#Image_file="c:\DES-3225G\3225run.b55"


Note that: # means comment only.
Make sure you point the directory to where the codes are stored - C:\DES-3225G\ is my example here.

You will need console connection to the switch.
You will also need a TFTP server running on the same PC at the time.


Before starting on the steps specified,
MAKE SURE you connect a serial port from the PC to DES-3225G.
MAKE SURE you have a fixed IP address for the PC - eg. 192.168.0.1
MAKE SURE you also set a fixed IP address (via console port) for the DES-3225G- eg. 192.168.0.100
Save Changes and then Reboot the switch for the new IP address on DES-3225G to work.
MAKE SURE you connect the network cable from your PC to DES-3225G as well.
MAKE SURE you have TFTP server program running (attached above).
PAY attention to the # sign in the config file. 


Hope that is not too hard for you to upgrade the firmware.