Ok this is a very important and common procedure - everyone will have to do it at least once in the life of their blade - yet it's very strangely not discussed and Silhouette does a poor job of telling you how to do it.
There's a video online telling you to ratchet the blade to 1, then 0, 10, 9... then it'll get very hard to turn and to continue to force it. It might work (didn't work for me), but it's overkill and disassembles the entire blade. There's a high risk of damaging your blade.
The easier way is to ratchet to 1, then 0, then maybe 10. The only point of this is to hide the blade to protect yourself. Next, the white part unscrews into 2 sections: