This question comes up a lot and there are a lot of answers out there. I wanted to note how I’m currently handling this, mainly since it gets undone when updating a standard included theme.
Go to the current theme’s folder inside wp-content/themes and edit the footer.php file. Search for the word “Proudly” and change that to what you need. In the style.css file, search for “wordpress.png” to change out the “W” icon.