You can choose the target grade in the beginning of the prep course. If you want to change it later, you can do it by changing your goal:

• If you use the WordDive mobile app, you can change your goal by tapping on the big picture icon on top of the course list. There is also a button on the very bottom of the app that will take you to the goal settings.
• If you use a computer, you can change your goal on the Exercise page by clicking the “Select Course” menu and then selecting your option in the Goal drop-down menu.

Don't change your goal repeatedly, however. Make sure you complete 100% of at least one goal so the grade guarantee will stay valid.

If you have already completed most of the first goal you chose, it is better to finish it first. If there is still time after finishing one goal, you can work on the other goal as well, free of extra charge.