If you need to configure proxy settings in order to access your Subversion server, you will need to set them using TortoiseSVN. TortoiseSVN is a free tool that allows you to execute Subversion commands directly from Windows Explorer. Before downloading and installing TortoiseSVN, please see the following article: http://casecomplete.zendesk.com/entries/20564722-shared-project-and-tortoisesvn-users-do-not-upgrade-working-copy-folders
Once you have it installed, right click on any package in Windows Explorer, and select Tortoise SVN / Settings. In that dialog, click on Network which will present you with the proxy settings.