Correction in Marksheets can be done for most of the boards. Now you didn't mentioned the name of the board in which you have studied your 10 and 10+2, so we can't provide you if or if not there are any instructions available online regarding this. Although I would say in most boards, such corrections are done with the records of the school. So you need to contact your school where you have studied your 10 and 10+2. The officials will guide you out. Also you can contact your District Education Officer regarding this, he/she can also guide you out.

I hope this answer helps. All the very best for your future endeavors!