The datamodel has changed with new versions of almost all packages. You need to upgrade the files first, then go to the apm and run all upgrade scripts that it offers you under 'Install Packages'. When the version of acs-kernel has changed then you are propably better off running only the kernel upgrade scripts first, then restarting the server and then running the remaining upgrade scripts.
That is the theory - I have not tried it yet on a dotlrn installation with real data and I am just answering this because no one else has yet so that you get at least a rough idea of what has to be done. It might be that after upgrading acs-kernel individually you need to do the same for acs-service-contracts.
Of course try it only on a copy of your database first!
Feedback about problems you run into would be highly appreciated.
<blockquote> If the database has changed after the upgrade, can we still use it
with the old installation?
</blockquote>
No.
<blockquote> Is it maybe possible to access the same database with an old and a
new installation at the same time?
</blockquote>
No.
