To flash new firmware you may be required to update the bootloader (TinyBooterDecompressor)
Note: When moving from 4.1 to 4.2 you must update the bootloader.
First, start MFDeploy. Select USB, the Netduino and then click "Ping" to verify the device is available:
Now click "Browse" and select both the ER_CONFIG and ER_FLASH files.(Hold down the "CTRL" key to select the second file)
Optionally, you can choose just "ER_FLASH" to upgrade just the firmware. If you choose to upload the ER_CONFIG file, and you have a Netduino Plus, you will need to reset the MAC address of your device by going to the Target->Configuration menu option.
Note: If you have flashed 4.2 firmware you must be in bootloader mode to set the MAC address. To enter bootloader mode disconnect the USB cable to the netduino, then reconnect the USB cable whilst holding the button down
The MAC address for your Netduino Plus is on the bottom sticker.
When both files are selected, click Deploy. This may take a while...
Once deployment finishes, detach and reattach your Netduino using its MicroUSB cable to complete the flash operation.
After flashing and rebooting your Netduino, you can now verify the version of the current firmware by selecting the "Target->Device Capabilities" menu option
This will output something like
SolutionReleaseInfo.solutionVendorInfo: Netduino (v184.108.40.206 b1) by Secret Labs LLC