TortoiseSVN for updating wordpress plugins
For updating wordpress plugins, and probably other SVN related stuff, i found that using TortoiseSVN is the easiest. For windows anyway.
Just go to the downloads page, and pick the correct flavour for your OS.
Run the installer
Just leave the default settings (usually)
And done, now you should be able to access the TortoiseSVN via your windows explorer.
Open windows explorer, and right click in a new folder (or an existing one if you like)
You should have the following additional menu items, to allow access to the SVN Checkout.
Add your SVN Details for checking out your repo, URL, Destination, and a password.
If its a wordpress plugin repo, it will probably have a URL something like: https://plugins.svn.wordpress.org/your-plugin-name/
Actually to check out, you dont need a password, only to commit changes.