After your Diploma you can take admission in B.tech. 2nd year directly and to get admission in IIT you can give IIT entry test but I don't know diploma persuing students after 10th can give IIT Entrance test or not.
You can search that in Internet and also ask your teacher and if you are eligible then this is the best option to get admission in IIT but you have to hard work.
If you can not give IIT Entrance test or UPSC Exam for government colleges then you can take admission in any private engineering college directly in 2nd year if possible for you and then do preparation for GATE properly and then aaply for GATE exam in your 4th year and after scoring very good score in that you can get admission in IIT to persue M.tech. if you are interested so far because after scoring very good in GATE you can get a good job in PSUs(HAL,GAIL,BHAIL,etc.) with very good salary package more then your expectations.
Best of luck.