Hello Iman. The first thing that will help you is to have an English dictionary always at hand. This will not only help you with spelling but also understanding. As you are going to college then you should raise questions there, but neither they nor anyone else can improve your memory - that comes with frequent use and repetition of anything that you find difficult.
There are various 'programmes' that are said to aid memory, but your case is much more about learning and using.