How to upgrade PHP 5.3.10 to php 5.6 on Ubuntu 12.04.5 LTS without upgrading the entire system?

Question

PHP

System : Ubuntu 12.04.5 LTS.
Php -v : PHP 5.3.10
Task:
upgrade php to version 5.6 without affecting other packages. (There is a joomla site that "breaks" after updating the entire system.)
Actions:
:~# add-apt-repository ppa:ondrej/php5-5.6
Cannot access PPA ( https://launchpad.net/api/1.0/~ ondrej/+archive/php... to get PPA information, please check your internet connection.
:~# add-apt-repository ppa:ondrej/php5
OK
:~# apt-get update
OK
:~# apt -get install php5.6
Reading status info... Done
E: Failed to find package php5.6-cli
E: Could not find package by regular expression "php5.6-cli"
E: Could not find package php5.6-common
E: Could not find package by regular expression "php5.6-common"
E: Could not find package php5 .6
E: Could not find package by regular expression "php5.6"
E: Could not find package php5.6-mysql
E: Could not find package by regular expression "php5.6-mysql"
E: Could not find package php5 .6-fpm
E: Failed to find package by regex "php5.6-fpm"
E: Failed to find package php5.6-curl
E: Failed to find package by regex "php5.6-curl"
E: Not failed to find package php5.6-gd
E: Could not find package by regular expression "php5.6-gd"
E: Failed to find package php5.6-soap
E: Failed to find package using regular expression "php5.6-soap"
E: Failed to find package php5.6-mbstring
E: Failed to find package using regular expression "php5. 6-mbstring"
E: Failed to find package php5.6-zip
E: Failed to find package using regular expression "php5.6-zip"
E: Failed to find package php5.6-mcrypt
E: Failed to find package using regular expression expression "php5.6-mcrypt"
E: Failed to find package php5.6-xml
E: Failed to find package by regular expression "php5.6-xml"
How to add a 5.6 rep or what can be done about it?

Answer 1

uninstall the old version and install the new one. Update the repositories.

Answer 2

buy a new vps/vds/cloud,
install php5.6 or php 7.2 with the new ubuntu :)
set up php, nginx (apache), mysql and everything else, transfer the site if it works without errors on the test domain test.mysite.ru , turn off the old one, load the latest database, if some data has changed, set up the domain for a new hosting.
ready!