Upgrading PHP on Wordpress install

Has anyone found any guides on how to upgrade PHP on their VPS Wordpress install and get Wordpress to actually use it?

Hello
I just installed Wordpress on the VPS but the PHP version is 5.6.40-0+deb8u12

Ive tried everyrthing to update it but still get the same problem
php7.0 : Depends: libapache2-mod-php7.0 but it is not going to be installed or
php7.0-fpm but it is not going to be installed or
php7.0-cgi but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

did you dinf any solutions yet?