Gregg

This plugin allows you to change the footer text on the bottom left of the admin page.
Once activated, navigate to the Settings -> nuAdmin Footer and change the Footer text/HTML. You can use html to link to your website, your help desk, your email or anything you would like. If you find the plugin to be useful and would like to donate, you can do so in the Settings.
Here’s a link to <a href="http://www.tripleginteractive.com/blog/wordpress/custom-admin-footer/" title="free wordpress plugin: custom admin footer" rel="nofollow ugc">the blog post on this topic</a> for more information. Future version’s will have much more capabilities.

nuAdmin Footer

This plugin allows you to change the footer text on the bottom left of the admin page.

Silkalns

WP Chill

Remove or replace footer credits (or any text or HTML in page) before page is rendered. With this plugin there is no need to modify code such as footer.php which if done incorrectly can cause your site to break or new theme updates will stomp over your changes requiring you to remove footer credits on each update.
This plugin has very minimal options to keep things simple and easier to use. You enter the text or HTML that you would like to find in one text box and the text or HTML that you would like to replace in another text box (or nothing to remove). Go <a href="https://cpothemes.com/remove-powered-by-wordpress/" rel="nofollow ugc">here</a> to view my step by step tutorial with screenshots and video.

Remove Footer Credit

It seems to work, but not as intuitive as it should be. You need to copy the code that makes up the footer porting you wish to move and paste that into the box. Wish there as a way to simply way to remove it.

Seems to Do Nothing

Remove or change footer credits or any text or HTML without modifying code.

nuAdmin Footer vs Remove Footer Credit