also here are two plugins

http://www.oxwall.org/store/item/368

this one says its for version 1.4 or below so make sure you ask the developer before you buy

http://www.oxwall.org/store/item/502

this one does not say a version so ask the developer before you buy.

good luck...

Touching on Aliia's  point and expanding that idea a bit here are two down and dirty ways without a plugin..  

Important - only attempt these if you know what your doing in the database, if not dont even try this.

Also i recommend getting the plugins that do this, they are worth it..

You can choose to have a test account just for this purpose if you want rather than use your account.  (As Aliia Stated)

1.  Change your password for admin to what you want the customers pw to be.

  Then go into the database to the user table and copy your new encrypted pw to the members pw that you want to change.

1a.  Change your admin pw to something new.

1b.  Notify the member of their new password.

2.  Have a little php file that you can run whenever you need to.  Again i caution you if you dont know what your doing and dont apply proper permission on this file someone can get your salt value and that is not a good thing.   I would suggest making the permission on this file min 600 and when you need to use it you can change it to 644 then change it back to 600 when you are done.

Create a file lets call it  get_newpw.php for example...  (dont use this name or every tom dick a harry in the world will be running your php file.)

2a.  View your ow_includes/config.php and get the value of your salt key....  every site has a different salt  look for

define('OW_PASSWORD_SALT', '############');

the # indicates the number that you want.  copy that number..

2b.. Now open your new php file you created get_newpw.php (or whatever you called it)and put this code  (never ever ever ever use a text editor like ms word or the like to edit a php file, they place special chars in the file and you do not want that), use notepad worst case, or preferred is  programers notepad or programmers notepad plus,  is perfect..  

<?php

$salt='paste your salt value here';
$pass="put the password you want here";  //example testpass1 dont use special char.

$testhash = hash('sha256', $salt . $pass);

echo $testhash;

?>

2c. Then run that file in your browser  yoursite.com/get_newpw.php and copy that new  hash and paste it to the user table for that member pw.

2d. notify member of new pw.

Done...