Hi Felipe - I was just promoted to 5th kyu (6 Feb. 2010). In our dojo 5th kyu is the 2nd test you take. My first test was for 6th kyu (that video is on YouTube as well.
Work on those rolls and falls! Exam or not, the better you can do them, the safer, more comfortable, and more confident you will be. Start slowly, slowly, slowly, and only increase speed and height when they start to feel easy and relaxed.
Here's a really good, quiet introduction to mai kaiten ukemi (front rolls) by Donovan Waite Sensei
, in case it's helpful. Also, of course, ask senior students at your dojo to help you learn. Having someone show you, and give you immediate feedback, is the best way.