Update Failed: The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions.
This issue is usually caused by incorrect file permissions on your server (rather than being a problem with the plugin itself). Basically, WordPress isn't able to properly access its own plugins folder, and as a result can't put the updated Divi Booster files in there.
It should be possible to solve this by following the instructions in this post:
In the "list of critical files and folders" make sure that the "wp-content/" and "wp-content/plugins/" directories are set to the recommended permissions.
If you're not comfortable doing this yourself, your webhost may be able to make the necessary permissions changes for you.
Once the permissions issue has been resolved you should now, if all is well, be able to update the plugin successfully in the WordPress plugins listing.