Hi! Thanks for helping. I'm going to try your steps.
Pick a template file.
Open it for editing.
Add the code below. The code needs to be added within php code blocks within that template file. Do not delete your templates existing code.
Visit a page on your website (frontend) that uses that template file (e.g. an about page that uses a template called basic-page, etc). www.mysite.com/basic-page.php
Your password (and optionally user name) will be changed.
Edit the template file in #1 and #2 above.
Remove the password change code.
Reupload the edited template file if it was edited locally.
Go to your admin URL and login with your new password (and new name if you changed it as well).
Before, I'm going to make a backup of files and database, right?
Thank you so much for help me!