As mentioned previously we have a system of hormone & brain interactions that work out the stresses we're under and relay the message to the brain. Our set point is calculated based upon the amount of stress we are under, remember stress isn't just having a hard time at work, its being dehydrated, malnourished, over exercising, blah blah blah. Our set point is there to ensure we always have adequate reserves to fall back on to deal with the stresses we're under.
If your set point works well and your leptin is giving the appropriate response (i.e your not in starvation) then when you accidentally eat more than you need, your body will receive a message telling it so, and also burn off the unwanted energy. So, how do you alter this set point? Quite simply you tell it there a no longer any stressors and you always give it the energy it requires to avoid going into starvation. Simple really, but I'm guessing your brain hurts a little so I will cover it in greater detail in another post soon.