I want to do a different course at the same uni, is it too late?

So I applied to do Media, Culture and Communication and got a conditional offer, then I realised this was a mistake and I wanted to do Journalism. You need the same grades to get in and it is the same university, would I have to go through clearing? And does that mean if I get an unconditional offer tomorrow I'd have to reject and go through clearing? Baring in mind I think the Journalism course is a little more competitive.
Thanks