Login to the Admin Panel, go to Developer->Database->Maintenance and click the Remove Sample Data button. Note: Please take a backup before removing the sample data. Don't use this option on a production site, this will also remove all your existing products, blogs and other information.
Go to Developer->Logs and click the Purge Cache link in the top right corner.
You can also clear the cache from the Summary Dashboard.
Yes, the location module contains all preloaded locations, if any of the location is missing, you can add it easily through the Admin Panel via Settings->Locations section.
Note: Do not delete locations from a production website, the location ID is stored in the Orders table.