PHP

switch php version ubuntu

# Interactive Way
sudo update-alternatives --config php

switch php version ubuntu

# From PHP 7.1 => PHP 5.6

#Apache
sudo a2dismod php7.1
sudo a2enmod php5.6
sudo service apache2 restart
 
 #command Line
 sudo update-alternatives --set php /usr/bin/php5.6

switch php version ubuntu

$ sudo update-alternatives --set php /usr/bin/php7.1
$ sudo update-alternatives --set phar /usr/bin/phar7.1
$ sudo update-alternatives --set phar.phar /usr/bin/phar.phar7.1

switch php version ubuntu 20.04

# This might be a longer process but it worked for me
# firstly completely remove the current PHP present in your OS (ubuntu)
# command to remove > sudo apt-get purge php7.*
# next command > sudo apt autoremove -y

# now install the php version you want with the command > sudo apt-get install php7.2 libapache2-mod-php7.2 php7.2-mcrypt php7.2-mysql