After being asked how to disassemble a Wacom Intuos4 pen, I've decided to write a separate post on this topic. In the photo below I've numbered each step in the exact order of how I disassembled each element of my Intuos4 Wacom pen.
1. Remove the pen circular head by unscrewing it.
2. Pull gentle the button and you should hear a click when it's out as it's fitted like a lego piece in 2 holes. by 2 plastic pins.
3. Slide gently the top half of the pen (the plastic grip).
4. This part should be easy as the bottom half of the pen comes out fairly easily (a.here in the eraser cap you should have 2 small springs that normally go inside of each other, b. there is a rail inside it through which you should slide the circuit board when you assemble it and it helps you to position it correctly)
5. This is the protective housing where the board is kept.
6. Slide gently the circuit board from the plastic main housing.
Please find the steps in the following image and if you need further help please do not hesitate to leave a comment or contact me by email. Best of luck and hope this helps you.