Step 1: find out if Astronomy is offered. From my perspective, it seems radio astronomy may be a close match to your present studies. So if you want to apply your electronics / communication, it could be to your advantage to pursue that avenue.

Step 2: If Astronomy is offered, look at the courses required for the BS in that field. The idea is to see how the courses you have already completed will be “accepted” or count toward the Astronomy degree. The more courses that count the better. If fewer courses count, then you may have more work to do, which may also mean being in school longer.

Step 3: Talk with an Astronomy professor and discuss your desire to change majors. Seek their guidance. They may have other suggestions for you.

Step 4: Talk with a counselor (if they are available…in US schools, this is a support service for students) about the proper paper work to file. If counseling is not available, maybe an Astronomy professor can help you.

Step 5: once the necessary paperwork is completed, you should be on your way to majoring in Astronomy and getting your degree.

Hope this helps you. Good luck in your studies.