You should have created a UKVI account so you can access your eVisa before the 31 December 2024, but the service is still available do this now if you haven't.
Some individuals will have received an email from UKVI with instructions to create an account. From 6 August 2024 the service was made available to everyone, so you do not need to wait for an email.
You can find out about eVisas and creating your account on UKVI's eVisa page. You can create your UKVI account starting on this page, Get access to your eVisa.
You must use your eVisa to travel to the UK, and you should ensure your current passport is linked to your UKVI account. Your carrier may also ask for a share code to prove your immigration status.
It is recommended to retain the expired BRP/BRC as it may help with future visa applications to stay in the UK, and for your personal records.