Ditto what ghia said. Here's what I do:
What it means is that you need to clear all the old files that are not index.html in the following directories:
Your site will rebuild what it needs after that. Also, you should have the standard index.html file in each for protective aspects (especially if it's inside the XOOPS_ROOT directory which isn't recommended, but some hosting services require it, although if that's the case, you need a better hosting service -- try noise.org
What I did was write a quick command line script for mine to run from the XOOPS_TRUST/xoops_data/caches/ directory
is replaced with an asterisk, which I can't use without getting IP banned)
Hope that helps.