BuddyPress.org

Try modifying some of these settings in /wp-content/plugins/bp-custom.php or in wp-config.php:

define ( 'BP_AVATAR_THUMB_WIDTH', 50 );

define ( 'BP_AVATAR_THUMB_HEIGHT', 50 );

define ( 'BP_AVATAR_FULL_WIDTH', 150 );

define ( 'BP_AVATAR_FULL_HEIGHT', 150 );

More info found here:

https://codex.buddypress.org/how-to-guides/changing-internal-configuration-settings/