Site Wont Work On Php7

Quite a long story but I made a schoolboy error.

I upgraded my dedicated server to PHP7 and mariadb 10.1

Before doing this I upgraded the sites on the server that needed it, to latest versions, but I left one as it already met the requirements..>WRONG it didnt it was 4.2.

So now im left with a site on the server that gives error 500 . All files folders etc are fine and still intact, it just wont work with php 7.

Question is whats my best option to access it and upgrade to latest version, Im thinking local machine using xampp then re upload to live server.

Anyone else have better solution, is new store and store import a viable option perhaps?

Cheers

John

Anyone else have better solution, is new store and store import a viable option perhaps?

First check the files and folders permissions (PHP will run a 500 error when dealing with any file or folder that has permissions set to 777), clear cache, enable the debuger and check the error messages/lines.