“ClassicPress automatic upgrades are guaranteed not to contain breaking changes by our versioning policy, and ClassicPress will never upgrade between major versions that may contain breaking changes (e.g. 1.1.0 to 2.0.0).”
Does the developer team intend to built a migration plugin from version 1.7.4 to 2.x (2.0.0), what allows an automatic upgrade?
First, you need the latest version of the Switch to ClassicPress plugin, which is what I linked to. If you have that, then open it via Tools → Switch to ClassicPress, and hit the button that says: “Show Advanced Version Control”. Then you should see another button that says: “Please select an Option”. You should now see ClassicPress v2 as an option. Select that and the update should start.
From here you would click on “Show Advanced Version Control”
Then you will see a page much like shown below and you would select
“ClassicPress v2.0.0”
then click
“Perform the Custom Migration now!”
Your site should now upgrade to v2.