I am not a techie, but have just done similar as part of a cyber resilience audit.

You should make the one you want to keep an "Administrator". Then using that one you can delete the other account. That assumes that you only want one account on your machine and that account can have full administrative rights. I have recently been advised that this is not a good idea!

The advice I have received was that I should keep my daily user account as a "Standard" user, and then in addition create a new "Administrator" account. Only the administrator is allowed to install new software, and so if a bad actor tries to download and install something nasty as an attachment etc then it wont automatically do it when you are within your "Standard" user account but will immediately flag up that an administrator account and password are required. That will alert you to the potential threat. Hope that makes sense?