How do I edit the copy on the portal/account popup?

My issue is I want all my content to be available to everyone, regardless of they’re membership level and whether or not their paying. But the portal/account popup has the following copy:

Your account

You currently have a free membership, upgrade to a paid subscription for full access.

I would like to edit this copy to something like “upgrade to support the site”. I’d assumed I’d be able to create a template file (like in this solution) to override it, but extensive searching is proving fruitless.

I’m using hosted Ghost(Pro) and my account allows me to edit themes.

Is there an archive of all the portal template files somewhere? (Not just the CTA mentioned in that post)

Thanks (and apologies if it’s right under my nose.)