In order to update your site you will first need to login. You will have been supplied your login details by email
The admin pages for WordPress are located at your normal home page + /wp-admin
Enter your username and password and click Login. The password supplied initially will be a long, randomly generated string of characters. After logging in for the first time, you can change this to something more memorable by going to your personal profile page. You will see your username up at the top right corner of the browser window. Click on that to go to your profile page, then scroll down to the bottom of the page and you will see the account management section.
Click on Generate Password to create a new random password like the one you originally received. You can then replace that password with one of your own choosing.
However you should be aware that it must show as a Strong password, otherwise it will not be accepted and your password will be unchanged. If that happens you will see a warning at the top of the page after you click Update Profile.
Advice on choosing strong passwords has changed in recent years, and best practice now is to use a pass-phrase, i.e. a combination of unrelated words which you can remember but others can’t guess. You can find further details on the WordPress website.« About WordPress Up The Wordpress Dashboard »