Stap 1 vertalen
First, carefully pull off the little plastic piece number 1. You must use a knife or something with sharp edge to wedge.
After this, you are ready to disassemble pen's exterior case, pulling strongly between parts 3 and 4. If it's hard, you can turn pieces 3 and 4 between them, but only a bit because electronics inside has a guide that lock it into the case.