I can’t log in as it’s saying my e-mail is not registered and I’m trying to change my password to a more memorable one, I’m not very computer literate so help would be much appreciated 👍

email password can be changed through a web browser and not from iPhone.

If you are referring to an Apple ID password (which also uses email) --> Click->If you forgot your Apple ID password - Apple Support

Change your Apple ID password

1. Tap Settings > [your name] > Password & Security.
2. Tap Change Password.
3. Enter your current password or device passcode, then enter a new password and confirm the new password.
4. Tap Change or Change Password.
5. Sign in with your new Apple ID password to access Apple features and services.

Change your Apple ID password - Apple Support