Is it possible to increase the capacity of human brain like “Lucy”? I saw the film "Lucy" in 2015. The film says that humans can use 100% percent of the capacity of their brains.

According to my personal ideas, the capacity of the brain will changed based on the basic knowledge of a person. We all know Albert Einstein was a great knowledgeable human in the world. This level of knowledge can change by the time, for example he was arguably the best scientist or philosopher of his time; he used his brain as much as possible for innovation.

At the present, there are many more scientists in the world, but the world is filled with knowledge, new technology etc. Man's basic knowledge could be higher than a scientist in the past, because this knowledge is openly available everywhere. But the problem is that they don't use their brain to the same level as Einstein or any other scientist that has lived in the past. That means that they don't use the highest capacity of the brain.

So according to my idea, the capacity of the brain will vary depending on external environmental factors. 

According to comments and suggestions in this article I read, I was unable to identify the truth: whether people can enhance their brain capacity like "Lucy". And I need to know whether humans have a fixed brain capacity or not. 

Most religions say that their saints had used 100% of their brain capacity. So what about other humans?
This may provide you with extra supplementary information regarding the notorious "10 Percent Myth". 
To respond to your statement regarding increasing brain capacity through am increase in knowledge:


  Synaptic Consolidation is the process by which items are transferred from short-term to long-term memory. Within the first minutes or hours after acquisition, the engram (memory trace) is encoded within synapses, becoming resistant (though not immune) to interference from outside sources. 


Knowledge has to do with "saving" the original memory traces followed when first learning the information. It does not necessarily have to do with active brain capacity. Thus, an increase in knowledge will not necessarily cause an increase in used brain capacity. 

You see, the primary issue here is energy cost. Although the brain typically only constitutes 2 percent of the body's weight, it utilizes around 20 percent of the body's energy intake. As a species, we have been "designed" through the filtering of many "versions" our species to be most efficient. As we have not found a particular need to utilize such a large percentage of our brain at a time throughout the millennia, our brains have been simplified into a somewhat energy-efficient structure, utilizing a portion of the total capacity at a time. However, if Man had originally needed to use more of the brain capacity for a majority of his or her daily activities, it would be safe to expect that we would use a larger portion of our brains at any given instance. Assuming you are still in a state of heightened neuroplasticity, it is potentially possible to "increase the amount of brain capacity used at a time" by participating in activities requiring multiple parts of your brain. 

But how many different activities can you think of that would require reasoning, planning, parts of speech, movement, emotions, problem solving, movement, orientation, recognition, perception of stimuli, visual processing, perception, recognition of auditory stimuli, memory, and speech?