Remove or edit author for posts

I have MultiSites. I import content from RSS feeds and write my own posts. So, I am not the author of all posts and I do not want my name listed as such.. I need to change "by toni" or just eliminate it site-wide. I am the only author on my all sites.

On the site with imported RSS content to post I added messages to the sidebar, before and after the content of each post, to make it clear: I import content without permission for my own use and please share/comment on original source site - not mine. I link to and credit the source. But "by toni" is still incorrect.

I am not WP tech literate or a coder - but I can follow detailed instructions.

Thank you