How to delete content from a WordPress installation

I had installed a theme which had provided some sample content. I had imported the sample content using the xml file and imported the images and other files linked in the content. However, I have decided not to use the theme.

Now I want to use another theme which also has some sample content. However, I realized that I have to delete the content added earlier. Is there a way by which I can delete the content uploaded earlier from the database before I upload the content file provided with the second theme.

I’m aware that this can be done manually by deleting all the pages and posts created. However, that would not delete any images or videos that have been uploaded. Those I believe can be deleted manually from the content folder via FTP. All I would be left with I suppose would be the categories that have been created. I can clean that table manually from the database. Is there anything else that needs to be purged?

Is there any script which I can run to purge the content?

Thanks in advance.