Never do 2 things at once. Since 4.4.2 supports PHP 5.6, I suggest doing the upgrade of Blesta first, then upgrading PHP.
Backup database + files
3.6->4.4 is a long way, I suggest upgrading to 4.0, then 4.4.2. See the upgrade docs at https://docs.blesta.com/display/user/Upgrading+Blesta for an important list of files that must be deleted when upgrading from 3.x.
After you are up and running on 4.4.2 on PHP 5.6, and upgrade PHP, then you will need to apply the right hotfix in the blesta-4.4.2.zip file, hotfix-php7 for PHP 7.0, and hotfix-php71 for PHP 7.1 or 7.2.