There are many reasons why we recommend against using backup plugins, and the massive and unwieldy backup files are one of them.
If you want to migrate your website, the most reliable way to do so is to just copy the entire WordPress installation. We’ve described this process here (specific for our hosting, but not WordPress):
WordPress’ instructions on how to move a site are pretty much the same:
This is easiest if you still have access to the original hosting account and website. If not, then you could choose to setup a local web server (with XAMPP or WAMP or something like that), import the backup there, and then migrate that site to our hosting.