The difficulty of each case is not objective and depends a lot on your academical background and preparation. I suggest my students to respect the order that is given and to consider the level indicated in order to evaluate your performance.
Even if you are at the beginning of your preparation a specific advanced case could help you to highlight your weak point or to be aware of what you should be able to do at the end of your preparation.
Please consider that especially at the beginning is not really important to solve a case in the right way: an hard case that you are not able to crack can teach you far more.
Hope it helps,