Firstly I'd backup the database and restore it as a new version for testing.
Something like websitename.umbraco7.cms
What details do you have on the database being corrupt?
This way you can break it as many times as required until you've got it right.
Then I'd just try upgrading the nuget package if that's an option?
the upgrade from 6-7 shouldn't be a massive issue and it will perform the database upgrade.
You'll need to ensure umbraco config is using Webforms rather than the default MVC razor views. see here for more info: https://our.umbraco.org/documentation/reference/templating/
If you prefer to work with Webforms, you can change the default
template engine in the /Config/umbracoSettings.config file, find this
section and set the type you'd like to use (Mvc or WebForms):
<templates>
<defaultRenderingEngine>WebForms</defaultRenderingEngine>
</templates>
Another option is to create a new clean solution and install the latest Umbraco version you are upgrading to. Once that is installed, reset the connection string to your current site database and set the umbracoConfigurationStatus appSetting to the version you are currently on.
<add key="umbracoConfigurationStatus" value="7.7.1" />
When you build and run the website for the first time, it will recongise you have umbraco already installed and will perform the update within this solution.
The clean umbraco install will default to using Razor templating, you may need to switch it back to webforms (see previous comment regarding this) or manually migrate the views from webforms to razor.
I can't express enough the requirement to do this away from the production database, make a backup and run through the process as many times as required until you've got a clean build.
If in doubt, consult the upgrade documentation: https://our.umbraco.org/documentation/getting-started/setup/upgrading/general
