You are free to quit at any time. Every training lecture sent to you will contain a unsubscribe link
We would always recommend you take a little time to think about it before you unsubscribe. A lot of students who quit return and sometimes they can get stuck in a cycle of doing this over and over again (which is something we deal with in the course).
If you just need a break, you can pause your studies and resume when you feel you're ready. To do so click "settings" in one of your most recent lectures you received