无法通过PHP代码更新wpdb

I am trying to update my database value but I am unable to achieve this. Basically I am trying to update a fields meta_value but don't know where I am wrong. I have inserted the below code in my theme functions.php file. Below is the code.

function update_values () {
    global $wpdb;
    $update_query = $wpdb->query("UPDATE wp_postmeta SET meta_value='10,15' WHERE post_id='1981' AND meta_key='cuzd-prod-general-v'" );
}

Try using $wpdb->update.

<?php $wpdb->update( $table, $data, $where, $format = null, $where_format = null ); ?> 

From: https://codex.wordpress.org/Class_Reference/wpdb#UPDATE_rows

In your case:

$update_query = $wpdb->update( "wp_postmeta SET meta_value='10,15' WHERE post_id='1981' AND meta_key='cuzd-prod-general-v'" );

try this out. Its pretty simple

update_user_meta( $user_id, 'nickname', $uname );

You can get the user_id by using get_current_user_id() function as

$user_id = get_current_user_id();

So your complete code will be

  $user_id = get_current_user_id();
    update_user_meta( $user_id, 'nickname', $uname );

Your meta key is "cuzd-prod-general-v" so use that key instead of 'nickname'