Your brain power can be modified, in either of two ways. One is positive and the other is negative.
For negative brain growth, drink and drug, eats lots of processed packaged food, get no exercise, do no learning, stress yourself frequently, and sleep irregularly.
For positive brain power growth, think the opposite.
Your brain is much more malleable than we ever knew until the Decade of the Brain, the 1990's.
"For at least a century before the discovery of neurogenesis (the birth of new neurons) in the adult human brain, a prevailing belief in the field of neuroscience was that the brain of virtually all mammals (not just humans) remained structurally constant throughout life and was incapable of producing new neurons." (by Tadzia GrandPré, PhD)
However we do grow new neurons, if we prepare the neuronal soil so to speak.
It appears however that new neurons do not spring forth fully prepared to solve philosophical or quantum mechanical problems.
They must be challenged by novel learning experiences, as Simon Evans, Ph.D. says, or "difficult learning" as by Tadzia GrandPré, PhD. says in her recent article in Adult Neurogenesis-BioEd Online Physical exercise is the most important aspect of growing your brain power, and by that I mean enhancing your brains neuroplastic or neurogenetic capacities.
Physical exercise does not mean you have to get all sweaty, and lift huge barbells off the floor. Actually you do not even have to roll barbells, you can get by with an exercise ball, or dumb bells and regular fits of HIIT, or high intensity interval training lasting all of 10 minutes.
HIIT, as Angie and Scott Tousignant teach it, can consist of calisthenics like you did in physical education classes in school, as long is you do 10 minutes of 30 second bursts of each one. Not sure about you, but to protect my 61 year old brain I can handle 30 seconds of jumping jacks.
Or as Evans and Burhardt say in Brainfit For Life, do more of what you are already doing physically, walk one more time around the block, or park further from the door of the shop you are going to.
Nutrition, including regular feedings of omega 3 fatty acids are very important for increasing your brain power.
The best source of omega 3 fatty acids is from fish, ocean going preferrably, definitely not farm grown, but including fish means you can risk mercury poisoning, so perhaps a supplement is in order. Just make sure the supplement says it has been processed in such a way that mercury is removed from the fatty oil.
Then eat lots of fruit and vegetables which have been vine ripened, for the full ration of phytochemicals, vitamins, minerals, fiber, and antioxidents, ect.
Your brain only weighs in at 2% of your body weight, but it consumes 20% of the fuel your body requires so a regular supply of nutrients including lots of antioxidants is a requisite. (Oxidative stress is a major cause of premature aging).
With physical exercise and nutrition covered, the next consideration for your brain power is 'difficult learning' or a novel learning experience.
This kind of learning, like the learning involved in learning a new language, or a new musical instrument, challenges the brain in increase connections between neurons (neuroplasticity) and demands that the brain bring the new neurons just born into the fold, usually in the hippocampus where memories are made.
Research about computerized brain fitness programs, one paper published in 2008, and another, called the IMPACT study, published in April 2009, indicate some real power in the dual n back task for increasing fluid intelligence and IQ, and from the Posit Science Brain Fitness Program for helping Senior Citizens, older than my 61 years, recover about 10 years of memory effectiveness, and both appear to generalize to other tasks.
So your brain power is very positively or negatively impacted by your lifestyle choices, including how you choose to challenge your brain.
For a look at four computerized brain fitness programs that offer the right kind of challenge and feedback to your brain, you can do no better than these. I own them and bought them for a bit of insurance for my own brain.