Using WP_Query to Show Posts Only From Certain Categories

I am trying to customize a portion of a theme that displays a slider showing all posts on the site. I want it to just show posts from a certain category, such as cat=1 or cat=3.

How do I edit this piece of code to accomplish this?
<?php while ( $wp_query->have_posts() ) : $wp_query->the_post(); ?>

Here is the full code for the slider.

<section id="fromblog">

				<span class="underline">
					<h2 class="section-title"><?php _e('Drink', 'albedo'); ?></h2>
				</span>

				<div id="fromblog-desc">
					<?php echo stripslashes_deep($theme_options['blog_desc']); ?>
				</div>

				<div class="fromblog-items-wrap">
					<div class="flexslider carousel">
						<ul class="slides">

							<?php while ( $wp_query->have_posts() ) : $wp_query->the_post(); ?>

								<li class="carousel-item fromblog-post">
									<?php if ( has_post_thumbnail() ) { ?>
											<div class="fromblog-thumb">
												<a href="<?php the_permalink(); ?>">
													<?php the_post_thumbnail('fromblog'); ?>
												</a>
											</div>
									<?php } ?>
									<h3><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h3>
									<span class="excerpt">
										<?php the_excerpt(50); ?>
									</span>
									<a href="<?php the_permalink(); ?>" class="readmore"><?php _e('Read More', 'albedo'); ?></a>
								</li>

							<?php endwhile; wp_reset_query(); ?>
						</ul>
					</div>
				</div> <!-- .fromblog-items-wrap -->
			</section><!-- #fromblog -->