Log onto Synergy. This change does not need to occur in canvas. However, be aware that students won't know their grade change.
Go to Gradebook --> Gradebook Setup
Click on Gradebook Settings.
Under drop scores, enter the number of grades you want to drop per category. For example, if you want to drop the lowest test grade for each student, enter a 1 in the box for assessments.
You will need to repeat this for each class or you can click the appropriate button at the bottom of the screen.