You’ll need to know how to change files on the server. If you have a local copy of WordPress that you uploaded, follow the instructions below and then upload (via FTP) the files to the server. If you know how to edit the files on the live site, you can make these changes there.
1. In wp-content/themes, create a new folder named responsive-child.
2. In that new folder create a file called style.css,
3. Put the following code into style.css:
/*
Theme Name: Responsive Child
Theme URI: https://example.com/
Description: Child theme for the Responsive
Author: Your name here
Author URI: https://example.com/about/
Template: responsive
Version: 0.1.0
*/
@import url("../responsive/style.css");
.powered {
display:none;
}
4. If you are working locally, upload the style.css (and its containing foler) to the server.
5. In the WordPress Admin, go to Appearance > Themes. There should be a new option “Responsive Child”. Select that and activate it.
6. The footer on the right should be gone.
See the Codex article on Child Themes for more information about making changes to a theme you’ve downloaded. This is an important feature of WordPress that lets you take advantage of updates from the theme author, but preserve your customizations.
Indeed, you can make more extensive changes (like changing that text the above solution just hides to something else more appropriate for your site). To do that you need to find the file in the theme that you need to change (in this case it is footer.php), make a copy of the theme’s version of the file in your child theme directory, make the changes and publish.
Best wishes.
PS: You may wish to add a Credits page to your site where you can acknowledge the work of the theme author.