Marcel,
"Database" in technical terms doesn't contain photos and videos, themes. It saves only links to them. Files themselves are saved in another place.
I think your idea is to export your whole site and not only the database.
This can be done via "Data Exporter" plugin.
For example you would like to export everything except "Spring" theme.
1. Copy and save "Spring" theme's files somewhere on your computer in case you will need them in future.
2. Change your current theme to another one ( for example "Origin") via the admin panel.
3. Delete "Spring" theme's files via FTP.
4. Install "Data Exporter" plugin, and export your files.
5. Install "Data Importer" plugin to import exported files.