A. You are an average student and you are thinking of changing to ICSE after your state board VII exams.
Many students join state board because parents would have enrolled them into it. Once they reach 10th , they start considering changing into ISCE or CBSE. If you want to change, now is the time because you would, initally struggle in 8th but pick up and do well in 9th and 10th exams
B. Before changing, please consider the positives that would add to what you have in hand at the state board.
With CBSE holding the JEE, NEET exams, CBSE has become very popular in India. The syllabus is tough, students need some extra coaching but it is worth it and competing at any exams after 12th ,national or international becomes easy.
ICSE has a slight different outlook in the sense that, it prepares the candidate with therotical knowledge and also the ability of how to apply it. Here, the lab and practicals have focussed imporatance. The other advantage is from 9th -12th you get to choose your subjects flexibily based on your future plans and subject strengths. The evaluation in ICSE is tougher than CBSE and state board. Hence scoring in ICSE is not evey easy. The biggest advantage of ICSE is the fact that this ciriculum prepares you on par with international education systems.
So, if you and your parents have plans of overseas education and job options as a key aim, then go for ICSE, it is expensive than state boards but you are better equipped to face your graduation and compete at the international levels for scholarships and jobs.
If you are keen on taking up the IIT route or the NEET exams for the medical UGs, then consider CBSE.