We lift ourselves by our thought.
If you want to enlarge your life, you must first enlarge your thought of it and of yourself.
Hold the ideal of yourself as you long to be, always everywhere.
-- Orison Swett Marden (1850-1924)
In any study, you lift your grade first by changing your thought.
If you want to "up" your marks in any school subject, you must see yourself capable of doing better, and replace your inferior complex with higher self esteem.
With that aspiration you have, hold the ideals and work towards what you long to be.
You will be able to do better in any subject if you wish to excel and put in efforts to close the gap between where you are and where you want to be!