Shifting to Commerce from Science after 12th is seen in many students and it is easy for you to change to your desired stream if you have interest and fervency in the subject and would like to make your career in it. Before changing or finalising about changing the stream, kindly go through both the stream again with these points:
a) Family pressure - Many families pressure their children to take up science as they want them to become a doctor or engineer but the children find it hard to cope up with the subject. Sit with your parents and make it clear about what you feel and make the changes.
b) Too hard to study - As science is a vast subject, without interest in the subject, it will be very difficult to get the concepts and round the clock, study routine to complete the topic is more exhaustive and this affect your grade, so need to rethink about it.
c) Its a bouncer - It is very difficult to understand what is taught in class and everything just bounces above your head and even mugging them up is not helping you to cope with the subject. Indeed, everything is not taught in class but this is common for all stream and you need to join any good classes for it instead of going for a change in stream.
d) The study, study, study - When we look at other stream students, i.e. Arts and commerce, you are not able to enjoy your college or other vacations or holidays as you have practices, vivas, assignments, etc which is known to everyone beforehand but if this is what is making you think about changing the stream, do have another go through your thought.
Even after pondering to the above 4 points, you feel that your passion lies in commerce and better suited for your life then surely make your decision and shift to commerce. You can be sure that only the 1st semester will have accounts based on the 12th std, all other papers will be theory and even the accounts papers will be new to all students that can be easily understood. Most of the topics will be Final Accounts i.e. preparation of Balance - sheets, Taxation, Economics, Finance, etc.
Some of the job opportunities in commerce stream are as follow for your reference: Chartered Accountancy, Company Secretary, MBA, Stock exchange, Banks, Insurance, Tax Consultant, mutual fund, Financial Planning, Logistics/Supply Chain/ Portfolio/Marketing/Hospital/Finance/Retail/Media/Rural/Infrastructure/Technology Management, Foreign Trade, many government jobs opportunities(Central, State, PSU after clearing their respective competitive exams), Defense, etc.