im 15 and doing my gcse's in the UK and ive chosen a subject which is public services over buisness studies. Ive heard if you get into buissness you earn alot of money per year through investments and other buissness stuff. i want to change my subject but i am not alowed due to it being half way through the year and i want the best career possible and a really good pay job so what should i do?

public services is like the police force and army but army you get bout £16,000 a year and i want like £50,000 a year.
any suggestions

thanks very much