LastPass doesn't show up in Safari after upgrading to Lion 10.7 or running Software Update for Safari 5.1. How can I install the new version?
This package will uninstall all existing copies of LastPass and upgrade your computer to the latest version that works with Safari 5.1 : https://lastpass.com/lpsafari_EOL.pkg
This link will only work on a Mac and you will need administrative rights on the machine to run the installer. This software package supports Safari 5.1 on OSX 10.6 Snow Leopard and 10.7 Lion.
If you are on a PC and need to upgrade, you can simply do so by going to this URL in Safari : http://www.lastpass.com/dl