I want to join in IIST after diploma there is one and only choice to write jee advance exam

The information you have is wrong. Actually Diploma holders are not allowed for JEE Main admissions but they are allowed for JEE Advanced. So they can write the JEE Main exam just to qualify for JEE Advanced. Since you have 10+2 and have passed out in 2016, you will be eligible on the basis of your class 12 marks only for JEE Main 2018. You wont be eligible from 2019 to appear in JEE Main or even JEE Advanced. So if you plan to write the exam after you complete the diploma, you wont be eligible. Instead you will be eligible to go for lateral entry as diploma holders go directly to the 2nd year of engineering. You can also write UPSEE I guess if you want to join B.Arch. For UPSEE you will be eligible for engineering on the basis of your class 12 marks and frankly that would be a waste of the diploma that you are doing. Please think over and then decide. You can write to us if you have further doubts.