[@ravey Participant 11 years, 7 months ago]

For anyone wanting to do this I figured it out.
Step 1: Go to your child theme and find /groups/groups-loop.php find the code that says

<div class="item-avatar">
				<a href="<?php bp_group_permalink(); ?>"><?php bp_group_avatar( 'type=thumb&width=45&height=45' ); ?></a>
			</div>

Step 2:
You will replace that code with “group-header” code found here(groups/single/group-header.php)

<div id="item-header-avatar">
	<a href="<?php bp_group_permalink(); ?>" title="<?php bp_group_name(); ?>">

		<?php bp_group_avatar(); ?>

	</a>
</div><!-- #item-header-avatar -->

That worked for me. Probably not the best route to altering it if you want to do a lot of CSS modifications to the “Group Forum Listing.” But if you want to just change the size to something larger this works.