To change/adjust the level or difficulty of a student's curriculum, you'd want to use Boddle's learning differentiation tool. You can figure out how to do that here.
Step 1: Click on the Student Manager (Students)
Step 2: Click on the "Change Curriculum" button
Step 3: Select the student(s) you want to differentiate learning for
Step 4: Verify your students and press "Next Step"
Step 5: Click on the Curriculum drop-down menu and opt to create a new differentiated path by clicking on "Create New".
You can also add the selected student to an existing curriculum path by clicking "Select Existing"
Step 6: The last step is to choose the new curriculum you'd like to differentiate to, and then click "Change Curriculum" to finalize.
Here is a video on how to change student curriculum: