Tips and tricks
WordPress Quick Tip - how to change default thumbnail size on theme activation
Write this in your theme functions.php
[php]if ( is_admin() && isset($_GET['activated'] ) && $pagenow == 'themes.php' ){
global $wpdb;
$wpdb->query("UPDATE $wpdb->options
SET option_value='145'
WHERE option_name='thumbnail_size_w'");
$wpdb->query("UPDATE $wpdb->options
SET option_value='145'
WHERE option_name='thumbnail_size_h'");
}[/php]