Logged into 2016 macbook Pro with old Apple ID how do I change it?

I haven’t used my 2016 MacBook Pro 7 or 8 years just turned on and I’m logged in using my old Apple ID, email is hotmail which I have used in 7 years. I’ve used my current id in all my apple devices since 2018. How do I change in this MacBook without losing my old data.

not sure if this it’s important there’s a pop up that reads “This Mac can’t connect to iCloud because of a problem with…has my old Apple ID email.

and because hasn’t updated in years another pop up reads “ iCloud Drive needs to finish updating before continuing to sign out”. It’s been uploading 1 item for 15 minutes now. I thought I could log out and then log in with new Apple ID but again want to access my old photos, back ups, and files.

Hope my explanation is understandable and he@rbfrom someone soon.

thanks from barely computer literate old lady