Dell SonicWALL GX250 Manual page 73

Updating Firmware Manually
You may also upload firmware from the local hard drive. Click Upload Firmware.
Note: The Web browser used to upload new firmware into the SonicWALL must
support HTTP uploads. Netscape Navigator 3.0 and above is recommended.
When firmware is uploaded, the SonicWALL settings may be erased. It is recommended
to save the SonicWALL's preferences so that they can be restored later. Once the
settings have been saved, click Yes.
SonicWALL Internet Security Appliance Guide Page 73