Upgrading Drupal

Good day,

I'm a greenhorn technical assistant at a public library and one of the things I need to do someday is get our site off Drupal 6. In order to test the migration, I've gotten a virtual machine going with a clean install of 8.6.1. I have all the web files copied over and I have the ability to connect to the Drupal 6 database from this VM.

None of my sites allow an upgrade. All were created with composer.

sudo -u www-data composer prohibits drupal/core:8.6.0
drupal-composer/drupal-project dev-master requires drupal/core (~8.5.3)
webflo/drupal-core-require-dev 8.5.7 requires drupal/core (8.5.7)
 

then

Hallo i've a Drupal Site 8.5.6.

I've upload ne new version Drupal 8.6.0 and my site now show this error

 The website encountered an unexpected error. Please try again later

In the error_log_php i've found this

 Uncaught PHP Exception InvalidArgumentException: "Field reusable is unknown." at /home3/papparec/public_html/core/lib/Drupal/Core/Entity/ContentEntityBase.php line 586

I'm not a novice and I'is the first time that i've an error when I upgrading Drupal :-(

I've just upgraded my Drupal 8.5.6 to Drupal 8.6.0. Everything is OK without errors until I run cron manually. I think that (in the past) I removed Drupal Commerce wrong way. This drove some modules, fields, enties,... to orphaned / obsolate thing.

Because of a beginner, so I cannot solve the problem by using PHP code from Drupal API guide as "programmatically delete a field".

https://imgur.com/a/rcYbg3W and https://imgur.com/a/swLGbag

I was trying to update my drupal... and got the next message:

drush up drupal
Update information last refreshed: Jue, 06/09/2018 - 21:56
Name   Installed Version Proposed version Message
Drupal 8.5.6             8.6.0            Actualización disponible

I updates core, vendor, and the php files manually. But when I run

php composer update

I get: