Migrate data to a fresh installation

Dear all,

At the moment I have a webshop running on 3.8 with customization. Because of this I can't do an upgrade to 4.2 or higher without getting into issues.
Now I also have a fresh 4.2 server running and I want to migrate alle published data (with all information per article like roles, product attribute, filters etc.) to the new server.  Is there a way to do this?
Also I need to migrate the customer information to the new server with all information. To make it easy for the customer I want to import also the password they use so they don't have any issues on the new server.
Does anyone has any experience in migrating from 1 server to the other or do you know who could help me on this?

Thank you in advance.

Regards,
Rutger

RE: " ... 3.8 with customization"
Did you make changes to the database?  (for example, add fields to tables?)

Hi, An external company did the installation, but as far as I know we don't have any changes on the database and only to the code.

If there were no changes to the DB, then you should be able to do the upgrade.  
First, backup your DB.  (And it's probably best to restore that to a copy/new DB and upgrade the copy).
Then apply each of the SQL upgrade scripts one after the other.  Then adjust the site's DB connection to point to the upgraded DB (in \App_Data\dataSettings.json) and test it.

Thank you. I will give it a try.