change on rule 269 of /includes/class-sidebar-login-widget.php
echo ‘<div class=”avatar_container”>’ . get_avatar( $this->user->ID, apply_filters( ‘sidebar_login_widget_avatar_size’, 38 ) ) . ‘</div>’;
change 38 to any pixel value you want.
This isn’t a good idea… changing plugin’s code is not a good practice. If you do this, in the future, each time the plugin is updated, you will have to re-code all changes in the new version.
If you’ve read the plugin’s description, you can see a filter to change the avatar size: sidebar_login_widget_avatar_size.
You can add a function to your functions.php file (in theme folder) to user that filter… for instance:
add_filter('sidebar_login_widget_avatar_size','new_login_avatar_size');
function new_login_avatar_size(){
return 50;
}
This will use an avatar of 50pt in sidebar login widget.