Need help upgrading 4.4.5 to 4.7.18 0n Ubuntu 16.04 server with PHP 7 on Drupal 7
Does your VPS let you choose the version of PHP?  If so, downgrade the version of PHP, upgrade CiviCRM, reset the PHP version.

Alternatively you could copy your installation to another server with older PHP, upgrade CiviCRM there and then transfer back to your VPS.

Since you have attempted an upgrade your system may be in a partially upgraded state.  You should start from the database dump and software tree that was backed up before the Ubuntu upgrade.

If you want to copy to another server, be sure to follow the instructions at Moving an Existing Installation to a New Server or Location.  You may want to get some help if those instructions look daunting.