Login to your WHMCS client area here> http://www.whmcs.com/members/ click on My Licenses/Services then click on the view details link to the right of your active license number and the download will appear there.
Also, please review the upgrade instructions here > http://wiki.whmcs.com/Version_4.3_Release_Notes
Hi,
To disable automatic registration, go to Setup > Domain Pricing change the registrar name to "none" in the automatic registrar dropdown on each TLD if you don't want to have the registration automated.
Roni