Delhi University (DU)

Yes, you can withdraw your admission from DU for another university. It will take almost one day, you can cancel your admission form online portal itself and then you can collect your documents from the college.

If you select PCM + English, then there will no deduction of percentage but if you take fourth subject as physical education, then your total percentage may get deducted by 2 - 3%. So, choose 4th subject wisely.

For comparison of the both colleges, you can use the college comparison tool:
https://www.shiksha.com/resources/college-comparison.

Which college are you interested in?

I don't think that is possible with because certain colleges in the university are not even allowing the migration amongst colleges.
All the best.

As per my knowledge, you should fill your choices in the application itself. Only you can choose the course.

Minimum qualification is 12th passed/appearing with 75% aggregate of best four including 85% in English for general category. A general candidate should have Minimum 60% in four subjects (including mathematics), 54% for OBC, and passing marks are required for SC/ST.

Yes, you can take this as your main 4 subjects.