Step 1: Click on "Edit Land" button in bottom left corner of screen.
Step 2: Click on Landcore in the island.
Step 5:
Click on "Apply" button to save your change
or
Click on "Reset" button to reverse your change.
Now you know how to modify your blueprint.
Step 3: Click on Blueprint from Inventory that you want to modify.
Step 4: Click on Modify" button.
Step 5: Click on Landcore in the island.
Step 7: Click on Landcore in inventory to replace with the old one
Step 8:
Click on "Apply" button to save your change
or
Click on "Reset" button to reverse your change.
Now you know how to modify your blueprint.