Thanks for your post and enquiry into taking over your mums account.
As mentioned by BenMcr, we don't offer a way of transferring the account in to another persons name. Your mum would need to contact us to cancel her account.
You will then be able to open an account in your name. It's worth noting that there would be a gap of 24 hours minimum in your services while the connection switches over. You would also get new equipment so if you have a TV service that has recordings on, it's worth watching them before hand 🙂