Can I use having a place on a course with lower requirements to change course?

Sorry for the confusing title.

What I’m asking is, can I change onto a course at university that has higher requirements than the course I have an offer for, because I’m already in?

I have an offer for law at a Russel Group university. I have/had pretty bad ADHD, most so in secondary school, so I only did foundation Maths and English. (I got a 5 in both)

I would much prefer to do economics but they require a 7, is there a chance that they would let me change course because I’m already in?

I have already called admissions about changing my course with no wiggle due to my grades.

Is there anything I can do?

*I am only considering University of … because A) I’m looking at breaking into IB/management consulting B) I want to stay home for the duration of uni to save money.

*I do not want to sound entitled, I understand that I am very lucky to have been given a place; however I want to be certain I’ll see it through.

*Only asking this because I was told by a teacher that this may be a way to do it.