If you use Mac OS:
1. Open Terminal.app, either by start typing Terminal on the Spotlight, or by going into Applications > Utilities > Terminal:
2. Open the hosts by typing on the Terminal that you have just opened:
sudo nano /private/etc/hosts
3. Type your user password when prompted (you can navigate the file using the arrow keys).
4. Edit the hosts file appending your new mappings underneath the default ones:
where IP_address is the IP address of your account on the server (it can be found in the Hosting Welcome Email), and domainname.com is your actual domain name:
5. Save the hosts file (when done editing the hosts file, press CTRL+O to save the file > press Enter on the filename prompt > Ctrl+X to exit the editor).
6. Flush the DNS cache (you can issue a simple Terminal command to flush the DNS cache depending on the version of OS X you are using and have your host file changes to take immediate effect).
NOTE: To revert the changes, you need to remove the new entries added to your host file or simply comment them by adding ‘#’ at the beginning of each line, then save the changes. You may need to clear your browser cache once again to ensure everything is fresh.