After unzipping, taring or whatever archive you used copy thepatch over the old files, replacing them.

Copy the files in your newly extracted directory (pmwik-new/wordpress-patch) over the files of your existing software installation. For example, if your existing PmWiki/Wordpress installation is in a directory called pmwiki/wordpress, then one way to copy the new files over the existing ones is to enter the command:

cp -a pmwiki-new/. pmwiki

Note that BSD systems will not have the -a option as a command-line argument for cp, but that's okay, since it's just shorthand for cp -dpR, so use that instead of -a.

On (some) FreeBSD servers and Mac OS X systems you need to use

cp -Rpv pmwiki-new/. pmwiki 

This works well on TxD shared hosting.

I found it really difficult to get svn via svn+ssh geting to work because I made two erorrs:
I used not my main user. However, only the main user can get shell access necessary for svn via ssh.
I used a wrong path.

In order to get things going set up subversion following the usual directives in the knowledge base and then access your repository like this:
(OS X terminal here)

% svn co svn+ssh://mainuser@yourdomain.tld/home/mainuser/svn/repositoryname/

This should do the trick.

Remember not to use ssh and http(s) at the same time. It's either or.