I don't want to go to uni anymore but I already accepted the offer?

Hi,

So I received an offer from University of Hertfordshire to study their film/television production course, alongside an accommodation offer. I paid the £400 deposit yesterday, however, after a long discussion with my parents, I've decided that I'm not ready to go to university and would rather do an apprenticeship instead, so I need to cancel my offer and get my deposit refunded. What am I supposed to do? Should I just call them up and tell them? It's still pretty early so I'm hoping I'm not too late as it hasn't been two weeks since my offer was made or my deposit was paid.

I'm thinking of maybe just deferring my application, so if the apprenticeship route doesn't go well, I could always go to uni next year without applying again. How do I do this?