Vesta CP comes with PHP 5.4 by default. If you want to upgrade it to 5.5, follow these steps

1. Stop Apache and Remove current PHP
[sourcecode language=”shell”]
service httpd stop
yum -y remove php
[/sourcecode]

2. Add remi repository
[sourcecode language=”shell”]
#For 32 Bit OS
wget http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
wget http://rpms.famillecollet.com/enterprise/remi-release-6.rpm
rpm -Uvh remi-release-6*.rpm epel-release-6*.rpm

#For 64Bit OS
wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
wget http://rpms.famillecollet.com/enterprise/remi-release-6.rpm
rpm -Uvh remi-release-6*.rpm epel-release-6*.rpm
[/sourcecode]

3. Enable Remi Repository
open /etc/yum.repos.d/remi.repo and add 1 beside enabled for both [remi] and [remi-php55], as shown in the screenshot

4. Install PHP 5.5
[sourcecode language=”shell”]
yum -y install php php-bcmath php-cli php-common php-gd php-imap php-mbstring php-mcrypt php-mysql php-pdo php-soap php-tidy php-xml php-xmlrpc php-pecl-apc phpMyAdmin roundcubemail php-opcache php-xdebug
[/sourcecode]

Step 5: Cleanup, linking and finishing
[sourcecode language=”shell”]
mv -f /etc/php.ini.rpmsave /etc/php.ini
mv -f /etc/roundcubemail/db.inc.php.rpmsave /etc/roundcubemail/db.inc.php
mv -f /etc/roundcubemail/main.inc.php.rpmsave /etc/roundcubemail/main.inc.php
mv -f /etc/phpMyAdmin/config.inc.php.rpmsave /etc/phpMyAdmin/config.inc.php
mv -f /etc/httpd/conf.d/roundcubemail.conf.rpmsave /etc/httpd/conf.d/roundcubemail.conf
mv -f /etc/httpd/conf.d/phpMyAdmin.conf.rpmsave /etc/httpd/conf.d/phpMyAdmin.conf
service httpd start
[/sourcecode]

And you’re done 🙂 Enjoy!