Hi, I applied to a PhD program in June and in september I was selected by a group leader of this program. I accepted the position confirming by email and they started preparing the contracts etc.I applied also to an other program in the same country and I find it more interesting.now they emailed me that I have been selected for the interview. What should I do?Can I go to the interview also if I've accepted the other position?can I tell the first group leader I don't want to join his group any more?

Go to the interview. They might not offer it to you or you might not be as keen on it once you hear more about it which would solve your problem. If they offer it to you and you want to go - I suggest going for it. These things happen! But you should tell them as soon as possible.

I would wait until after your interview before telling the first project leader as you will be in a better position to decide. If you get offered the second position that you are more interested in go for it as you need to be focused and really interested in the project to do it for your PhD for a few years, especially during slow parts of the process when you are waiting for results etc... Good luck.

thanks a lot, I will go to the interview!