#get latest package and check md5sum

wget http://wordpress.org/wordpress-2.8.6.tar.gz
md5sum wordpress-2.8.6.tar.gz
lynx -dump http://wordpress.org/wordpress-2.8.6.md5

#if md5sum is OK (should be 1956f09f2abe74ed85e0de04d511d433), then continue 

tar -zxf wordpress-2.8.6.tar.gz
cd wordpress
cp wp-includes/version.php /replace_your_wordpress_directory_here/wp-includes/version.php
cp wp-includes/js/swfupload/plugins/swfupload.speed.js /replace_your_wordpress_directory_here/wp-includes/js/swfupload/plugins/swfupload.speed.js
cp wp-includes/functions.php /replace_your_wordpress_directory_here/wp-includes/functions.php
cp wp-includes/formatting.php /replace_your_wordpress_directory_here/wp-includes/formatting.php
cp readme.html /replace_your_wordpress_directory_here/readme.html
cp wp-admin/press-this.php /replace_your_wordpress_directory_here/wp-admin/press-this.php
cd ..