I accidentally bought a 5V/16Mhz (the [9218), when I really needed the 3V/8Mhz unit (the [9220).
Unfortunately, I’ve already soldered the thing in place and don’t have time to wait for another one. 
I’m sure I need to swap the resonator – what about the regulator? Any help or advice would be greatly appreciated.](http://www.sparkfun.com/products/9220)](http://www.sparkfun.com/products/9218)
Looking at the schematic, it appears the only difference is the resonator and the regulator. I’m sure you would need to flash the 8MHz bootloader also.
I went over the diagrams and confirmed that the only differences are the regulator, crystal, and the silkscreen. Just make sure you use the 3.3v ftdi board so you don’t destroy any 3v3 devices hooked up to our board.
1. You need to unsolder the crystal and the reulator. You then need to solder the new ones on. Make sure it is a pin for Pin replacement.
2. You can find the 8mhz bootloader on the product page I believe.
Have fun 
Thanks, all, I ended up destroying the board trying to replace the regulator, so I bought another one. Very disappointing overall.
so i dont know if this is ~really~ a valid answer but…
what if you just apply 3.3 volts to vcc. then with the wrong resonator on the board, you can monkey around with the “board” in the arduino software to get something to operate at your desired frequency. or do some adjusting in your code to make it equivalent.
im suggesting this because i made a few projects with a 5v pro mini. i also used a nice external 5v regulator to power them through the “RAW” pin. so i didnt realize i was applying a very nice 5v to the “RAW” which then dropped it to 3.5±V? Things were working good enough but something seemed off till i figured out i should apply the 5V to the vcc pin. all better. but the good enough makes me think you could do the same on purpose.
i know it doesnt matter cuz you fried your board. just sharing.
-b