If you have problems* downloading it, please check these articles first.
In any case, to download Voicemod you have to go to http://www.voicemod.net/downloadVoicemodAccount.php and create an account with these options (soon more):
After logging in, the download will start:
Finally, when the installer is downloaded, just double-click the executable to start the installation.
*Although to start using Voicemod you must login anyway, if you have problems downloading you can download it directly from here: https://www.voicemod.net/downloadVoicemod.php