You mean they're just in one of your site's folders without being used by B2? I don't think B2 can tell which are not being used. You're probably going to have to delete them manually.

Hi Thank you for your reply
I posted those pictures , have used them on blogs and then decided remove those blogs, but pictures still appear in the section where I upload pictures for posts
but there is no delete button to get rid of them
How do I delete those pictures that are not in use

If you know which files you want to remove, it may just be a case of deleting them via an FTP connection.

Having gone back to my own blog, I can see that I do have the option of deleting files. I'm using v2.4.7, but it would seem an odd piece of functionality to remove in 3.x. I'm wondering whether this might be a blog permissions problem, or perhaps whether there is a problem with the installation itself. Failing that, my previous suggestion should work.

but there is no delete button to get rid of them

Do you have permissions to delete files? You can also delete old blog folder from /media/blogs/ directory to get rid of all files.