You can change the grade levels you teach in Mystery from your account management page or from the grade drop-down in the top left corner of the page when logged in.
Changing grade levels in account management:
This will change the grade levels for your account.
1) Click on your name in the upper right corner of the screen while logged in.
2) Click on "Account & Membership"
3) Scroll down to the "Profile" section and select the grades you teach, then click "Save"