II have passed 12th in arts stream. Can I do 11th and 12th again with a different stream, i.e. science?

Yes, you can repeat class 12th again with different stream but it is not advisable as it will hamper your career. But if you want to repeat it again with different stream you can do by submitting your 10th documents in college or school at the time of admission. As so many college offers to get dire

It's up-to you that if you want to study your 12th again. If you are willing to give another 2 years for 11th and 12th you can continue by submitting your 10th class documents like The marks sheet. You can enter any course you need and get into it as a fresher.