Default Role Change

Hello,
How do I update the default user upon registration ‘Custom’ role which is the name of a self-created user role I would like to use instead?
Thank you,

Why don’t you use an s2Member role and just change its name?

See General Options -> Membership Levels/Labels

I am not trying to make the name a priority, I am using the ‘Custom’ role I created with specific user roles.

I want this to be used as the default for new user registrations. How can this be done?

You are essentially doing it backwards. You should use an s2Member role, then customize the capabilities it provides using a plugin like Capability Manager Enhanced.