You can easily import a database backup via phpMyAdmin.
First of all you need a Backup (usually in the form of a .sql or .gz file)
Then you can log in directly to the database via phpMyAdmin by clicking [Webhosting] -> [Databases] in your control panel and right there next to your database Click the "Database icon".
Once you're logged in, make sure the database is selected in the left column. On the right you have to be able to see all the tables that are in the database.
Please scroll down to the bottom and select "Delete Tables" (or "Drop Tables").
You can now click "Import" at the top and select the backup file under "Select file". If you click "OK" below, the import process starts.