Hi Alexandre, my name is XXXXX XXXXX XX.XXX-XX, Your online expert ready to assist you
Thanks for the pictures & hey no worries, this is a common issue that comes up and an easy fix : Just need to loosen the bolt on the inside of the tank that hold the handle in place. Then go down to your local hardware store and pick up a replacement (click here) for a few bucks.
reference video > http://www.youtube.com/watch?v=DVgzvqUR7q8
~ Please give it a try and let me know if have any questions along the way with a reply....only rate my answer ok, great, or EXCELLENT after we have worked on the issue together to your satisfaction. Bonuses are welcomed & appreciated. I look forward to any future inquires as well, Thank You ~ Dr-Fix-It-Advise.com