Studying is like exercise. When you learn new information, your brain changes in much the same way that your muscles change when you exercise on a regular basis. If you want to lose weight or to change the shape of your body, you have to exercise regularly. Similarly, if you want to learn something new, you have to exercise your brain by reviewing the material on a regular basis over an extended period of time.
Exercising your muscles for six hours, one day a week is not going to produce a significant change in your muscles or your weight, but if you exercise one hour a day for six days and keep this up for several months, you will see results. The same goes for studying; six hours spent cramming the night before a test is not effective, but studying one hour a day for six days will help you to remember more and will increase the likelihood that the information is moved from your short-term to your long-term memory.
Get into the habit of studying on a regular basis. Create a 7-day calendar at the beginning of each semester, identify study times and a study place that you will visit at the same time each week, and write those study times on your calendar.