Upgrading to PHP7 can be done quite smooth. Just use the following commands. First add the new repository for PHP7:

$ apt-get install python-software-properties
$ add-apt-repository ppa:ondrej/php-7.0

Now backup any custom config files since we will remove PHP5 and install PHP7 now:

$ apt-get update && apt-get purge php5-fpm && apt-get --purge autoremove && apt-get install php7.0-fpm php7.0-mysql

At this point, php5-fpm should be removed and the php7.0-fpm service is running. It is, however, unlikely that your website is running properly – because the PHP-FPM socket file will have changed. If you’re running Nginx, you must update your fastcgi_pass directive inside your VHOST from:

fastcgi_pass unix:/run/php/php5.0-fpm.sock;

to:

fastcgi_pass unix:/run/php/php7.0-fpm.sock;

Some Nginx instances runs as the user/group nginx, if thats true in your situation you need to change the php-fpm file:

nano /etc/php/7.0/fpm/pool.d/www.conf

edit

listen.owner = nginx
listen.group = nginx

You might also want to change the user and group at the beginning of the file. If you had www-data in php-5, you can just keep this default.
Now restart nginx and php-fpm and it should work properly:“

$ service php7.0-fpm restart
$ service nginx restart

For LAMP, you should be able to just update through apt-get:

apt-get install -y language-pack-en-base
apt-get install python-software-properties
dd-apt-repository ppa:ondrej/php-7.0
sudo apt-get update && sudo apt-get dist-upgrade

This is what worked for me.

This is what worked for me:

sudo apt-get install -y language-pack-en-base
sudo apt-get install python-software-properties
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update && sudo apt-get dist-upgrade
sudo apt-get install php7.0
sudo apt-get install php7.0-mysql