From
https://openacs.org/doc/openacs-HEAD/upgrade-overview.htmlThere's an easy way on that page, if
* Your OpenACS Core is 5.0.0 or later
* You do not keep your OpenACS site in a local CVS repository
* You do not have any custom code
And if any of those is not true, there are many less easy ways on the following pages in the doc.