windows 10 login linked to an older email, how do I change this?

Before starting, I suggest you make a new system image or, at least, if you do not already have an additional [spare], local, Admin, password-protected user account then make one. You'll be able to get back in control of your computer with that if the changes you desire go horrendously wrong.
Add Local Account or Microsoft Account - TenForumsTutorials
Change to Admin account type - TenForumsTutorials

I always make sure I have two spares.
my ditty - Create two spare local, password-protected Admin accounts [post #2] - TenForums

Back to the changes you want to achieve:-
Either

Create a new user account and link it to the new email
and then make it an Admin type account if required
Add Local Account or Microsoft Account - TenForumsTutorials
Change to Admin account type - TenForumsTutorials

or

Convert the existing user account to a local user account
and then convert that to an MSAccount using the new email.
Switch to Local Account - TenForumsTutorials
Switch to Microsoft Account - TenForumsTutorials

All the best,
Denis

---

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I'm glad the problem has been resolved.
I do hope you make an additional [spare], local, Admin, password-protected user account. User profile corruption does not get reported anywhere near as often as it did for Windows 7.

All the best,
Denis