About deleting unnecessary attachments

How can I delete the attachment that is no longer needed?

For example on a wiki, there is a file uploaded like this.

![Foo1](/uploads/xxxx4e6794d257b0effbccb20cc935fa/foo1.jpg)

I have changed this to the following.

![Foo2](/uploads/yyyy4e6794d257b0effbccb20cc935fa/foo2.jpg)

“Foo1.jpg” is no longer necessary. In this case how can I delete “foo1.jpg”?