Very simple to do Cacti upgrade
wget http://www.cacti.net/downloads/cacti-0.8.8g.tar.gz
mysqldump -l --add-drop-table cacti > cacti.sql
mv cacti cacti_old
tar xvf cacti-0.8.8g.tar.gz
mv cacti-0.8.8g cacti
Restore old data to new installation
cp cacti_old/include/config.php cacti/include/
cp cacti_old/rra/* cacti/rra/
cp -u cacti_old/scripts/* cacti/scripts/
cp -u -R cacti_old/resource/* cacti/resource/
cd cacti
chown -R www-data:www-data .
In file include/global.php change option $url_path
Go to http://cacti_url/
Done!