This workflow assumes the quizzes are separate grade items in one category. For example, Quiz 1, Quiz 2, Quiz 3 Grade Items under Category Quizzes and that each quiz has the same number of points (10, 100–any number as long as they are all the same). 

1.  Go to Grades from Assessments or Course Admin on the Navbar
2. Click on the Category heading, not any of the grade items, (and not the dropdown context menu beside it). For example Quizzes (if that is your category name).
3. You should now see Edit Category in the upper left in big letters.
4. Scroll down to Distribution
5. Change number to 1 for lowest non-bonus items to drop for each user (see below). [if you want 2 lowest quizzes dropped, enter 2, etc.]
6. Click Save and Close