Did you install via One-Click?
To uninstall Joomla:
1 remove Joomla installation folder from your directory.
2 remove database created during installation if any
To reinstall, go to DH panel --> Goodies --> One-Click Installs. When you see the option to create a new database, you can use an existing database or create a new one for Joomla. Usually we suggest to create a new database for Joomla.
Note: You can manage Joomla database via DH panel --> Goodies --> Manage MySQL
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