Update a pre-existing Wordpress blog

Noob question but I’ve offered to update someone’s blog for them. They already have a domain name and content on the blog but she wants it to look more clean and modern looking. How do I gain access to customize her Wordpress blog. Do I simply ask for her login info and go from there? Any help is appreciated. Thanks

You’ll most likely need ftp access, especially if backend theme editing is disabled. If she doesn’t know what ftp means, then ask for what the hosting sent her (cpanel or similar).

Yes you can only access it if you have the credentials. Make sure to take a full backup before you start playing with the live site.
Start with updating the WordPress installation then update plugins and go from there.