how do i download the sism 3 expansion packs

if you have  Origin installed on your computer log into your Origin account from the shortcut icon of Origin on your desktop log in with your email and password you use for your account  in the my games tab find the icon right click-download

see also the new layout of the ep/sp http://answers.ea.com/t5/The-Sims-3/FAQ-New-Origin-Layout-for-The-Sims-3-Expansion-Packs/m-p/4641393#U4641393

and the new manager see the FAQ manager http://answers.ea.com/t5/The-Sims-3/The-Sims-3-Expansion-and-Stuff-Pack-Manager/m-p/4937010#U4937010