Index: wp-includes/capabilities.php
===================================================================
--- wp-includes/capabilities.php	(revision 40261)
+++ wp-includes/capabilities.php	(working copy)
@@ -677,6 +677,18 @@
 }
 
 /**
+ * Rename an existing role.
+ *
+ * @since 4.8.0
+ *
+ * @param string $role Role slug.
+ * @param string $new_name New role name.
+ */
+function rename_role( $role, $new_name ) {
+	wp_roles()->rename_role( $role, $new_name );
+}
+
+/**
  * Retrieve a list of super admins.
  *
  * @since 3.0.0
Index: wp-includes/class-wp-roles.php
===================================================================
--- wp-includes/class-wp-roles.php	(revision 40261)
+++ wp-includes/class-wp-roles.php	(working copy)
@@ -209,6 +209,26 @@
 	}
 
 	/**
+	 * Rename an existing role.
+	 *
+	 * @since  4.8.0
+	 *
+	 * @param string $role Role slug.
+	 * @param string $new_name New role name.
+	 */
+	public function rename_role( $role, $new_name ) {
+		if ( ! isset( $this->role_objects[ $role ] ) )
+			return;
+
+		$this->role_objects[ $role ]->name = $new_name;
+		$this->role_names[ $role ] = $new_name;
+		$this->roles[ $role ]['name'] = $new_name;
+
+		if ( $this->use_db )
+			update_option( $this->role_key, $this->roles );
+	}
+
+	/**
 	 * Add capability to role.
 	 *
 	 * @since 2.0.0