Yes, you need to add the Grandaughter as normal user then change to admin.
reboot to set GD as Admin see a)
You would have to perform the steps-
a) Login to your default account.
b) Click on the “Windows logo” and type “User Accounts”.
c) Now, select “Settings” and then select the “User Accounts” icon.
d) Click on “Manage another account” and then select the user account that you want to delete.
e) Click on “delete the account”.
f) Depending on whether you want to “Keep the files” or “delete the files” choose the appropriate option.
g) You can delete the other accounts similarly.
Note: Once deleted, the user accounts cannot be recovered. Make sure you back up any data if required.
Do let us know if you need further assistance. We will be happy to help. We, at Microsoft strive towards excellence.
Thanks.