Heidelberg University

Yes, you are eligible to join Heidelberg University for Master's degree in medical physics. Good luck.

You need to give IELTS exam, then you can apply for admission there.

Hi Durgesh, extremely good academic record is required. If you had work experience you must submit necessary documents. There is no language requirement for the course but you may opt to learn German language. In addition you must demonstrate high level of quantitative skills, relevant projects, publications, excellent recommendation letters, personal statement etc. Best you see this
https://www.uni-heidelberg.de/courses/prospective/academicprograms/mathe_ma_en.html.

No, you cannot do that.you've to start again with 1st year if you want to change course . Make confident decision this time so that you don't have to think about changing things again.

Hi,
Difficult to comment without knowing your profile. It is best you check with them directly or contact DAAD India. Here are relevant links:
https://www.ph-heidelberg.de/en/bachelor-master/bachelor-in-early-childhood-and-pre-primary-education.html
https://www.daad.in/en/study-research-in-germany/studying-in-germany/bachelor-studies/.