I had a bitfury bluefury and I could overclock in bfgminer by changing oscillator bits by pressing M and then O while bfgminer running. Stock is 50 which runs at about 2 gh/s. By changing to 53 or 54 you can achieve 2.5 gh/s. This also works on a redfury and icefury. Any higher you will need additional cooling.
The soldering option may also work as mentioned above ( thanks to Colin Miner for detailed advice ) but this might be an easier option.
Can you give us a step buy step please.
by pressing M and then O while bfgminer running
You can't get any more step-by-step than the original post.
It didn't work for me on a gnu/linux BFGminer 3.9.0 or various other versions I tried, I don't get a response from M then O, on a Bitfury BF1 so I stuck with the pencil mod.