I have two installations on two seperate sites and would like to know what the best version upgrade method would be.

I first site has OSclass 8.0 running and upgrading this site is not to important

The second site has a much older version of OSclass (I'm not even sure which version 2/3 maybe) I would very much like to upgrade this site ASAP to the latest version or at the minimum version 8.0. How can I replace the files so that I do not remove the current adverts and the email alerts that go out?

First, download Osclass and unzip the archive, then transfer all files and folders to the server with a complete replacement, except for the "oc-content" folder, you can't touch it!. Then go to admin panel and update osclass