How Export/Import new data, changed while working on upgrade?

[betterlead]

Scenario:

I have my live shop running on J2.5 & VM2.6.
Abouth 4 weeks ago I took an Akeeba backup, installed and upgraded almost everything and have a couple of test sites running pretty good on J3 & VM3 (On localhost and on a remote server in sub folder).
Since 4 weeks have past, there luckily has been some commerce going on i my web shop. New orders, new users a s o.

To my question: Is there any good guide on how to update the data that has changed in Virtuemart? Export from the live J2.5/VM2.6 site and import to the test site running on J3/VM3 - finally to take over as the new live site shop.

I have never done something near to this before, so I need to find a rather basic tutorial for this, if you know what I mean...
Could it be, in phpMyAdmin? Exporting tables? Then which ones? How?

[GJC Web Design]

You've actually created a bit of a problem here..
You can't just copy tables across as one is J2.5/VM2.6 - the other J3/VM3

And it isn't just VM data - you need the joomla users data and the linked info that goes with it

Personally I would try clone the old one -
upgrade to VM3
check everything
upgrade to J3
check everything

Now in theory you have  usable database tables that you can over write (obviously a test copy) the tables of your new site

just J user tables and VM user / order tables
even then u may have problems with things like ship, tax, payment ids in orders if these are different between sites

how many users/orders are u talking about?

another approach could be export the users/orders etc by e.g. csvi and see if importable

or a Joomla user importer for the users - then try the VM2.6 user/order tables directly in VM3  - may be then use the Update tables button in VM tools

[betterlead]

That was not very uplifting news. Isn't the need for this procedure very normal? Well I mean, you can't just close a working web shop for a couple of weeks and lose income - it certainly takes some time to do this upgrade and migration - especially if your not a pro on this and have to run your shop/business daily, beside from working on your site.
So, there must be something else I am getting wrong here. Much wrong..?

[GJC Web Design]

Obviously it is a problem if you have a large time lag with the updates ..
My work flow is normally clone old, do updates - check everything  (normally 1 hour depending on templates - at least get VM2.6->VM3 working)
Do live site.. then your max down time is short

Then you can continue on the clone  - solve template issues - J2.5->J3.0 at your leisure
And do the live J2.5->J3 again when quiet  and you know the issues

But as pointed out above - it is a suck and see situation - you know what u have - and there are different approaches to solve the problem
You have limitless opportunities to clone and test and see what works