It should be under your Internet Options, under Connections (If you are using IE).
Instructions
Internet Explorer
Open Internet Explorer. Click the "Tools" button and then select "Internet Options." This opens a new configuration window where you can find your proxy settings.
Click the "Connections" tab. In this tab, click the "LAN Settings" button.
Click the "Use a proxy server for your LAN." In this section, you can view your HTTP proxy server settings. Firefox
Open Firefox. Click the "Tools" menu option and select "Options."
Click the "Network" tab in the window that opens. Click the "Settings" button.
View the configurations in the section labeled "Manual proxy configuration." This is your HTTP proxy settings.