Hey hamiltino,
For Netregistry, there is probably not a php.ini file in your root directory already. Simply create a blank file (preferably in an editor like Notepad++) and include the following code.
upload_max_filesize=64M
and change the 64M to whatever you would like it to be. Then save it as php.ini and upload it to the root directory of your server.
Then, backup your .htaccess file (download a copy of the working version to your hard drive just in case), open it up and add the following code
suPHP_ConfigPath /home/USERNAME/public_html/
replacing USERNAME with your CPanel username. Save it and upload it back to your server. This should successfully change the upload limit for you. If after uploading the modified copy of your .htaccess file you have problems accessing your site, just upload the backup copy you downloaded before and replace the one that is up there to get everything working again.
Let me know if there are any questions on this.
Cheers,
Michael