Hey Manisha

If you've applied to a college and now you don't want to take admission there, then you can simply cancel your application. In this case, your whole application will not get rejected, only the application for the college that you've applied for will get rejected.

You can apply to other colleges as per your preference. If you've already taken admission in a college then you'll be eligible to get admission in other college only in the case when you withdraw your admission from the previous college where you've already taken the admission.

Thanks