Upgrade PHP version to PHP7 quickly on LAMP environment

Run Following commands:

$ sudo add-apt-repository ppa:ondrej/php
$ sudo apt-get update
$ sudo apt-get install -y php7.0

After that run following command:

sudo apt install php libapache2-mod-php

Now restart  Apache server :

sudo service apache2 stop
sudo service apache2 start

Repository required to install phpmyadmin

sudo add-apt-repository ppa:ondrej/php5-compat