My computer rebooted to factory settings and I don't know system passwords or set ups?

My computer had to be rebooted back to factory settings and I had to get the entire hard drive replaced. Before, I had a user account with specific password. Now, it has been relegated back to "apple1" but I don't know what the password is or how to find it.

As well, the user account can't be changed and the hard drive disk is labeled as "Untitled 1" and I don't know how to change it so that I can add things and reorganize my computer.

Any help would be greatly appreciated.

Thank you.