I am trying to update software and it is asking to sign in as administrator

The account you're logged into is usually an "admin" type account (there needs to be at least one of these in order to manage the system). The update process, needs your authorization to download and install the new version of the OS, and you should give it your password when it asks for authorization, otherwise you can't do the installation of the new OS.

You can open the System Preferences and click on the User&Groups item, then in the list of users on the left, underneath each username it says either "Admin" or "Standard" depending on how that account was created. If you only have one account, then it must be an Admin account.

If you need more info, just ask...

Good luck...

Typically, the account that you used to setup a Mac when it it is brand new is the administrator account. open System Preferences, and click on the Users control panel. you should be able to see the accounts on your Mac. One of them will be the admin account.

If you don't know the admin password, here's some tips to try.

https://tidbits.com/2018/07/05/three-ways-to-reset-a-lost-admin-password-in-high-sierra/