Do you access to your theme’s functions file?
Yep, I’ve got complete access over the whole website and hosting.
In which case this is the easiest way.
create a directory on your theme called ‘bbpress’
ie wp-content/themes/%your-theme-name%/bbpress
where %your-theme-name% is the name of your theme
find
wp-content/plugins/bbpress/templates/default/bbpress/loop-single-topic.php
Make a copy of this file, and put in in the directory called bbpress that you created above, so you end up with
wp-content/themes/%your-theme-name%/bbpress/loop-single-topic.php
bbPress will now use this template instead of the original
and you can amend this
so go to line 60 which says
<span class="bbp-topic-started-by"><?php printf( __( 'Started by: %1$s', 'bbpress' ), bbp_get_topic_author_link( array( 'size' => '14' ) ) ); ?></span>
and change the ‘size’ => ’14’ to a larger number for instance ‘size’ => ’20’
Instead of going through each template and possibly changing this, you can also use a php code function listed int this topic.
https://bbpress.org/forums/topic/resizing-avatars/#post-148625
The original source of their code seems to be from this guide.
https://schaltgetriebe.wordpress.com/2014/04/06/increase-avatar-size-in-bbpress/
