how to remove a link content from sidebar?

There are literally thousands of WordPress themes – which means that many people won’t be familiar with your particular theme. So a link to your site where people can see the theme might result in more responses.

Where can I remove it in Twenty Eleven theme?
Thanks!

You wouldn’t edit the Twenty Eleven theme. It is the default WordPress theme and having access to an unedited version of the theme is vital when dealing with a range of site issues. You would create a child theme for your changes.

Oh, yes, I’m in Twenty Eleven Child. Sorry did not mention it.

Impossible to say without a link to your site.