Hi Aditya.

Changing your abruptly in 11th standard is not advisable, but it is indeed possible if that is what you want. You can change your stream from Science in 11th to Commerce in 12th, but it depends on various factors. You will have to take approval from your affiliated Board, which is HSE in your case. Then, seat availability will be checked and permission from your school will be taken. The process is tiresome and sometimes stream change doesn't even happen, but it surely is possible.

All the best.