[support] New drupal administrator - can't find Site Building -> Modules

I have just moved and taken over the administration of a Drupal (6.16) web site. It's all working OK but, among other things, there are a number of modules clamouring for security updates.

I've read around the documentation and I think I can see the basics of how to do it (I have shell access to the hosting site which makes things relatively easy). However there is one rather fundamental problem (or at least that's the way it looks to me at the moment), there is no Administer -> Site Building -> Modules page. I have the other Administer -> Site Building pages, it's just the Modules one that is missing.

Can anyone point me in the right direction to fix this please.