Chris G wrote:
Well, I have now updated this Drupal 6.16 site to 6.22 and have also updated dozens of modules which were out of date to get rid of all the security warnings. It was fairly straightforward once I realised that, in the main, all that was needed was to download and unpack the relevant module tar file and copy it over the old version. I also read the release notes and did any extra cache clearing etc. mentioned there.
Just be aware that the copy over method for contributed modules may not be what you want to do. I highly suggest instead to remove the old directory and then install the new one. The reasons are varied but you can have a module that creates new directories or renames files or both and have more than one version of files in the directory.