You can change your IP address on your Mac OS X using your browser. If you are using Firefox, begin with the steps below. If you are using Safari, skip to step 4:
1. Select Preferences on your Firefox browser menu.
2. Select the Advanced tab on Firefox and click the Settings button on the "Configure how Firefox connects to the Internet".
3. Select to tick the "Manual Proxy Configuration". And then tick to check the box "Use this proxy server for all protocols". Under the No Proxy for box, input the localhost, 127.0.0.1. Go to Step 7 for the HTTP Proxy and Port. Click OK to save and exit. And then skip to Step 8.
4. To hide the IP on Mac using Safari, select the Preferences under the Safari menu.
5. Select the Advanced tab and then click Change Settings under the Proxies.
6. Choose Manually on the Configure Proxies option. Tick the check boxes Web Proxy (HTTP) and the Secure Web Proxy (HTTPS). Enter localhost, 127.0.0.1 on the Bypass proxy settings for these Hosts & Domains. Go to Step 7 for Web Proxy Server. Click Apply Now.
7. When using Firefox and safari, you need to input the IP address of the proxy server that can be used for relaying internet traffic for the HTTP Proxy (Firefox) or Web Proxy Server (Safari).
If you will just surf web pages and you don't need to log in to any site or use personal information, then it is good to use free relays such as http://www.publicproxyservers.com/. If you will need to log in to any site, use a paid proxy service such as iPrivacy Tools.
You are done! To go back to your regular connection, just do the first few steps above and then remove the proxy server IP information. Under Firefox, select No proxy on step 3 and on Safari, untick the boxes Web Proxy and Secure Web Proxy on Step 6.