add-apt-repository ppa:ondrej/php
apt-get update

This will install additional PHP packages, not only basic ones (including APCu caching, FPM, Curl …)

apt install -y php7.2 php7.2-cli php7.2-fpm php7.2-common php7.2-curl php7.2-gd php7.2-xml php7.2-mbstring php7.2-mysql php7.2-apcu
a2dismod php7.0
a2enmod php7.2
a2enmod proxy_fcgi setenvif
a2enconf php7.2-fpm
service apache2 restart