Work Life Balance

It has passed more than half a year since I started to work for the school.
What I think these days is how I can shorten the time to spend for work.
My current job starts at 8:00 a.m. and ends at 4:15 p.m. and I cannot change the fixed time.
However, starting from next school year, I strongly hope to shorten the time for work.
Although incomes would decrease, increasing my free time is more important.
During the free time, I will study English and read books more.
Currently, no stamina is left after work and it is difficult to take enough time to study.
I am wondering how I should manage my time for work and personal life.