Hi Carolina, you  can add or remove challenges at the beginning of each fasting week.  Before you start your week, you can scroll down and there you will see  that some challenges have already been added to your week. They are suggested to you based on your goals and progress. You  can also delete them by clicking on the waste bin icon and all the way  at the bottom you have the option to "add challenges". Please notice that it is not possible to change challenges once you have started your fasting week.