Can I give improvement exam of all subject next year in up board class 12th?
Yes you can surely give improvement exam to improve your scores. Students who got low marks in higher secondary can apply for improvement exam to enhance their score. You will be issued a new mark sheet after improvement exam. But as you are asking that whether you can give it next year, so it's not possible, if you have passed your 12th this year,you are eligible to seat for improvement this year only within a specified time. Aslo if you score less in your improvement exam it won't effect because than previous marks would be continued.
Hope it helps.