Wrong choices at A level!! HELP!!!!

[bossboggle]

DS takes 4 subjects at A level, first year. Is managing with most but realises he has made wrong choice in one!! Advice please . Did anyone else's DC do this and what happened? Should he change or what??

Thank you people for all of the advice!! Just to confuse matters DS has just done some sort of test in the subject he is not happy with and he has gained a grade B!! I think he will have to make up his own mind and as soon as too!! My DS doing maths mechanics too - no problems!! Oh the decisions that have to be made!!!!!