Can I eligible for JEE MAIN & WBJEE Exam after completing Diploma in CSE Branch ?

Yes, you will be eligibile JEE Main exam. foor this you will have impoorve and excel in the respective subjects and pre pare yourself for JEE Mains and JEE Advanced. The best thing tthat you  can do is sit for LEET ( lateral entry entrance exsamination)  this will help you in sharping your skills in fundamentals too. you will have commence your course like the other students who have completed their 12th.  For WBJEE, you will have to be in between 17 years of age till 25 years.