To put it plainly, you already are yourself. It is by definition impossible for you to not be yourself because, well, you are yourself, but that’s not the answer you’re looking for.
The sentiment behind “being yourself” is that you should not pretend to possess [or not possess] qualities which are not a part of your behaviour and that you should chase your passions and aspirations, do what you want to do and not limit yourself by conventions and such.
The mistake that many people make is that they identify themselves with their habits and qualities. You are not your qualities or habits, they are merely your possessions. Habits can be made and un-made. Accepting what you are right now as your perfect self would stunt your growth, you will not be able to improve yourself.
Now to answer your question, you can ‘be yourself’ by making yourself free from greed and the myriad influences which the world and the society have on you. Do things for the sake of doing them. Do things which make you lose your sense of who you are. Do things that engross you so much that you forget about your own existence and become one with the activity, the experience.
You ‘be yourself’ by losing yourself.