If you need to change one of your WordPress user passwords but are unable to access the WP admin account, you can make the change by editing your theme's functions.php file.
First, SFTP in to your server and navigate to the following path:
where APPNAME is the name of your WordPress app and ACTIVETHEME is the current active theme on your site.
Next, open functions.php and add this after the first <?php line:
wp_set_password( 'new_password', 1 );
where new_password is the password you want to set for the account and 1 is the number of the user ID in the wp_users table.
Save functions.php back to your server.
Now, you should be able to log in to WordPress with that new password.
Be sure to remove that change from your functions.php file or else every login request will keep resetting the password.