Hi there!
This is definitely something that your Uni admissions team can help with so I would get in contact with them. I wouldn't recommend asking to go from y1 biomed straight to y2 maths, as year 1 is usually where basic concepts are taught, so you may have missed out on some maths fundamentals.
You will normally be able to swap courses within the University as long as you meet the requirements for 1st year entry (grades/subject requirements). You might need a reference from a tutor/head of course to be able to swap so I would keep that in mind.
As well, you will have to retake a first year of Uni, and so only have 3 years of student finance left (you get the length of your first course + 1 year). This means that if you change courses a 2nd time to a third degree, or have to retake any years then these will have to be self-funded - not likely to happen but just something worth knowing!
Hope this helps!
Jorja (LJMU Student Rep)