Can I change the theme name in WordPress?

All the above is correct, but is not enough. After you rename the theme, e.g. rename the folder old-theme --> new-theme, you should copy the theme customizations (colors, header / footer, widgets, etc.) from the old theme to the new theme. This is done directly in the MySQL database:

1. Find an option named theme_mods_old-theme in the table wp_options
2. Copy the option_value (it is a text holding the theme customizations in a special WordPress format)
3. Put the copied value in a new option named theme_mods_new-theme in the wp_options table.

I changed my theme name in wp-content/themes/{your site name folder}/style.css I am using a child theme

/*
Theme Name: WhateverYouWantToNameIT
Template: twentytwenty 
*/

The answers above are good, but I wanted the full list and this is it so go to: wp-content/themes/{your site name folder}/style.css and change this values if they exist, if not you can add them

/* this should be at the top of your theme CSS file

 Theme Name:   Twenty Fifteen Child
 Theme URI:    http://example.com/twenty-fifteen-child/
 Description:  Twenty Fifteen Child Theme
 Author:       John Doe
 Author URI:   http://example.com
 Template:     twentyfifteen
 Version:      1.0.0
 License:      GNU General Public License v2 or later
 License URI:  http://www.gnu.org/licenses/gpl-2.0.html
 Tags:         light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
 Text Domain:  twentyfifteenchild
*/

See Source for more details

Its absolutely easy and simple, just follow instruction
1. Just rename theme name with your desire theme name.
2. open your desire theme name and open style.css file, and find theme name and changes with your desire theme name.
3. you can see your desire theme in admin dashboard-> appearance-> themes, just select and activate it.