Dear aspirant;

There will be no problem concerning you jeans pant. Just make sure there will not be any huge metal pieces in your Jean. Jeans pant is permissible but any sort of pants with metal pieces are strictly prohibited.

Again I would suggest you to wear light and tight. It will help you concentrate during the exam day. From my experience of JEE mains there will not be any problem if you wear jeans pant with casual shirt. Just make sure there should not be any huge metal pieces.

Hope this helps and all the best!