php -v
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update
apt-cache search php7.1
(optional) sudo apt-get remove php7.0
sudo apt-get --purge autoremove packagename
dpkg -l | grep php7.0
sudo apt-get remove "^application.*"
sudo updatedb # <-- updates the locate database (index). harmless
sudo locate application # <-- locates the file 'application'. harmless
sudo rm -rf (file/folder name) # <-- removes files/dirs recursively. dangerous.
sudo apt-get install php7.1 (from comments)
sudo apt-get -y install php7.1
sudo apt-get -y install php7.1-mysql
sudo apt-get install php7.1-fpm
apt-get install php7.1-curl php7.1-xml php7.1-mcrypt php7.1-json php7.1-gd php7.1-mbstring