<p>i have a windows client and i want to upgrade subversion from 1.5.3 to 1.5.4.  are there installation steps. . do i just copy the zip and extract and override the existing directoies ..  i can't find any clear upgrade instructions . . </p>

Which windows client are you using?
TortoiseSVN's upgrade path for me so far has been pretty flawless. You just download the latest installer, run it, and get back to work.
The only time I had an issue was upgrading from 1.4x to 1.5x, you
do
have to restart the computer after this installation, otherwise you'll start getting all sorts of funky errors because the Tortoise SVN in memory cache will be out of date and incompatible.
After a restart everything was fine. The repositories always get auto-upgraded, and unless there's something in the changelog saying otherwise, you can upgrade worry free.
Upgrading the client side of things should be a low concern anyways, just make a backup of your working copy, perform the upgrade, and if you do have problems, checkout the project into a new folder, move any changed files in, and your all set.
Upgrading the repository could have more ramifications, but again, I've yet to have a problem on that side of the system.
Having backups is a good fail safe.