How do I remove a category from a wordpress loop>

You can add category id or category slug into arguments you are passing to query_posts:

<?php
    // category slug ('products')
    query_posts(array(
        'post_type' => 'post',
        'showposts' => 5,
        'category_name' => 'products'
    ) );
?>

or

<?php
    // category id ('3')
    query_posts(array(
        'post_type' => 'post',
        'showposts' => 5,
        'cat' => '3'
    ) );
?>

In the second case you can use comma separated list of category ids like 'cat' => '3,5,7'.