i am presently doing b.tech 1st yr civil engineering but i want to be an aerionautical engineer.how can i switch from civil to aeronautical engineering and will it be helpful to me.

I am happy that you have not waited longer. All engineers take almost the same classes the first 3 semesters. Does your University offer aeronautical engineering? If it does, it is just a mater of going to your adviser and discussing it with him/her. It should be easy and smooth. If it does not, on the other hand, you have to apply to another university.