switching courses

It's usually up to the university, not UCAS, if youre talking about switching courses within the same university. Usually they are quite flexible if the course you want to switch to has similar modules and they may consider other things if the new course has specific requirements eg specific A-level results in a subject. It's more flexible at the start of the term and they will less likely consider your request later on in the academic year. As far as I'm aware, if you want it to change via UCAS, you should be emailing them now and requesting for the transder and it will update on UCAS although this might take a while and, again, it depends on the university.