changing php version
Wordpress might be fussy about which version of php it wants. Let's say it wants php7.1 specifically.
Type the following commands:
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update
sudo apt-get install php7.1
sudo apt-get install php7.1-cli php7.1-common php7.1-json php7.1-opcache php7.1-mysql php7.1-mbstring php7.1-mcrypt php7.1-zip php7.1-fpm
sudo a2dismod php7.2
sudo a2enmod php7.1
sudo service apache2 restart