The myth that we only use 10% of our brains has been debunkedhttps://www.scientificamerican.com/article/do-people-only-use-10-percent-of-their-brains/
The primary means of exercising our brains to improve analytic ability is education, and there are strategies for enhancing memory such as mnemonics.
However, the consensus about 'brain training' products is that they have limited impact. https://www.scientificamerican.com/article/brain-training-doesn-t-make-you-smarter/
The myth that we only use 10% of our brains has been debunkedhttps://www.scientificamerican.com/article/do-people-only-use-10-percent-of-their-brains/
The primary means of exercising our brains to improve analytic ability is education, and there are strategies for enhancing memory such as mnemonics.
However, the consensus about 'brain training' products is that they have limited impact. https://www.scientificamerican.com/article/brain-training-doesn-t-make-you-smarter/
It may be that, at any one time, we only use a certain volumetric percentage (though where 10% came from, I don't know) - just the same as your computer, your house or the electronics in your car - but that certainly does not mean there are huge tracts of unused neural real estate. Neurons that don't get used, die off, as they get starved of resources.
Oddly, the energy consumption of a sleeping brain is remarkably similar to that of an alert brain.
So, as Ed has answered above, the way to improve brain function is to exercise it - and look after the oxygen supply, of course (which generally means physical exercise) - oh, and sleep, of course.
Also as Ed answered, "brain training" really only makes you better at the sorts of tasks that come up in brain training - there's no transference to general tasks and abilities.