Hello , 

For appearing in the IAS exam the first necassary thing you need is to have an Graduate degree. As soon as you complete the degree you can appear for the exam. But you can start your preparations from now side by side, by joining any coaching centre. If you belong to Delhi NCR then i can suggest you best coaching institues of these localities for knowing comment in the comment box. Even if you dont feel like preparing from now or you cant manage both coaching and Bsc. then you could drop for one year after completing BSc. But till then you must buy a book for aptitude and reasoning and prepare that side by side.  It is very easy and is common in many competitive exams.

hope this helps 

Hii dear, 

The first eligibility criteria for giving an IAS entrance examination is that you should be hold a minimum a graduate degree in any of the courses or degree..

So, You should complete your bsc graduation degree and then you can prepare yourself for the IAS exam by taking a one year drop and taking a coaching from good institute, or else if you are so much keen to prepare for IAS, then you should prepare yourself side by side with your bsc course  this may be little bit difficult  but not impossible

You can easily achieve your dreams if you are fully dedicated to it. 

Hope this helped. 

Good luck.