Note :
Make a note of all changes you made in custom templates & delete it. As older templates will be replaced with newer version.
How To :
rm -rf /var/www/html/template/en/custom/*
Download Bugzilla
cd /root/
wget http://ftp.mozilla.org/pub/mozilla.org/webtools/bugzilla-4.2.tar.gzBackup Existing html folder (or bugzilla folder)
cd /var/www/
tar zcvf bugzilla-40.tar.gz html/Take MySql Backup
cd /root/
mysqldump -u root –databases bugs > bugs_back.sqlExtract Bugzilla
cd /tmp/
tar zxvf /root/bugzilla-4.2.tar.gzCopy Content of bugzilla-4.2 to html / bugzilla folder
cd /var/www/html/
cp /tmp/bugzilla-4.2/* ./ -rfva
cp /tmp/bugzilla-4.2/.bzr* ./ -rfva
cp /tmp/bugzilla-4.2/.htaccess ./
chown apache: * -RVerify Module dependency & run checksetup to complete upgrade
cd /var/www/html/
./checksetup.pl –check-modules
./checksetup.pl