HEllo,dear

Well diploma holder can take direct admission in Btech, but if want to do btech from IIT or NIT colleges .yes,it's possible but the procedure for everyone is common you have to appear in in jee mains first and then crack jee mains after that you have to crack jee advance to go in IIT's.it will be quite difficult for you .anyway wish you all the best!

hope this will help you!