I would leave the current PHP 5 on the local bedroom server and treat them as an archived version. Do not make any changes to the PHP 5 source files or try to install the latest server and PHP version.
Create a shared Free Online Server and upload the archived files to the online server.
On your local living room Php 7 server, download the old archived PHP 5 files, modify, validate, upload, overwrite the online shared PHP 5 archived files.
Browse to the online latest PHP 7 files and use the free w3.org online HTML and CSS validation tools.
Report back on encountered problems and/or successful upgrade.