Thank you.
Actually, in Word the default file location is the one I usually use. It is just when I want to save something elsewhere, say from the internet, it defaults to Tosh.

Certainly, I shall not delete ntuser.dat

Apart from your own saved files in 'Documents' in the Tosh directory there are other system files. All the ones in 'App Data' for instance. The computer and the Registry knows they are located there (under that name). If that name were to be changed, the system wouldn't know where to find those files. You'll notice that the option to rename that folder is missing, probably so it can't be renamed and upset the whole interlinked system.

As said though, files can be saved to any folder you want and just ignore the Tosh location.

If you really want to remove that name, there are ways but they might be thought too much trouble. Just do a search using the term 'change name of user folder windows 10' to find out more. I did and came up with these step by step suggested methods.

https://thegeekpage.com/rename-user-folder/

I'd probably do it by going into the User Account Settings and creating a new User or Admin account with the name I want. Transfer my saved files to it and then remove the Tosh account.

Don't delete it yet, JBR!

As has been suggested, it is, possibly, a user account which has been used to log in to Windows.

Many people use this to give their families, etc., their own W10 log in.

First, important check, I suggest is to try this once you're up and running.

1) Right click on the bottom left corner of your screen.- you should see "shutdown or sign out"

2) Left click to sign out.

3) Now, you're out of windows - click the screen and you should be offered the option, or options to log back in.

Is there an option called Tosh? (usually you will be looking at a blank screen with one, or more sign in options in the bottom left corner. The middle of the screen will be waiting for the pin, or password, to be used.

Are there other options (there could be several where guests have been allowed to have their own accounts)

4) If there is an option called "Tosh" there will also be folders, in File Manger, which lead to files being stored in Tosh.
If there are other logon names, there will be similar for them.(only accessible when that person logs on)

The name (e.g Tosh) can be changed in the Windows settings. Just log back in to go and change it.

Be careful about deleting as you may be deleting all that you have saved since you had the laptop.

Note:-

If you bought this laptop, with W10 already installed, it's possible that the dealer just makes a habit of using the "Tosh" for all the pcs he builds.

In that case, all you might need to do is to go into settings and change the name from Tosh to something you like better.

You can't really delete anything in the Users and Tosh directories unless there is an alternative/duplicate account with everything set up in it the way you want it. Do you keep a safe backup of your files on USB sticks or removeable drive?