Can I change my A-level?

Good evening,

So I have gotten myself into a mess. Up to about a week ago, I was sure that taking French will increase my chance of getting into LSE. But my mum has phoned them and they said that having a science is better for your application. Now I have considered taking chemistry instead but decided on biology because I find the content straight forward and score easy A*s. It's also very interesting and I found this Human Sciences course in Oxford that I could possibly do if I had gone off economics (my current amibition).
Therefore, I would like to change the French to Biology. I have sent 2 applications via UCAS last Friday and they were acknowledged but no respose yet; one of them was to my school's sixth form. I am about to send another one in but on paper to the college directly. Can I chose Biology in that application even though I picked French in the two other ones? To let you guys know, this college to which I'm giving a paper form would be my first choice.
Also, can I somehow change that French on my other application forms on UCAS, or do I need to wait until the interview and then explain myself? And will they be okay with it? I have an A prediced in core and additional science (2nd set) and B in French but aiming higher...
I have asked one person whose daughter went to my frist choice and she says that you can definitely switch. But I need to be sure. Have any of you been in a similar situation?

Thank you so much everyone for your time.

Good evening,

So I have gotten myself into a mess. Up to about a week ago, I was sure that taking French will increase my chance of getting into LSE. But my mum has phoned them and they said that having a science is better for your application. Now I have considered taking chemistry instead but decided on biology because I find the content straight forward and score easy A*s. It's also very interesting and I found this Human Sciences course in Oxford that I could possibly do if I had gone off economics (my current amibition).
Therefore, I would like to change the French to Biology. I have sent 2 applications via UCAS last Friday and they were acknowledged but no respose yet; one of them was to my school's sixth form. I am about to send another one in but on paper to the college directly. Can I chose Biology in that application even though I picked French in the two other ones? To let you guys know, this college to which I'm giving a paper form would be my first choice.
Also, can I somehow change that French on my other application forms on UCAS, or do I need to wait until the interview and then explain myself? And will they be okay with it? I have an A prediced in core and additional science (2nd set) and B in French but aiming higher...
I have asked one person whose daughter went to my frist choice and she says that you can definitely switch. But I need to be sure. Have any of you been in a similar situation?

Thank you so much everyone for your time.