Database Backup Restoration

Hello,

To make a long story short, we hired a company to make modifications to our website but have since disappeared from the face of the earth. We have access to the admin dashboard of the site and I have used the plugin to make a full backup.

They were making these revisions off of their own domain/server.

So my question is, our website is for example http://www.mysite.com and they designed this on http://www.theirwebsite.com . What changes would need to be made before i try restoring our site with their revisions on our server?

Would admin password remain the same as it was on their site or on ours?

Some direction here would be great!!

https://wordpress.org/plugins/backwpup/