Try this, open Safari/Safari Preferences, General tab, where it says "Save Downloaded Files To:" select Desktop from the dropdown menu. If Desktop is not there, click other, then select Desktop from the left side bar.
Then try downloading the standalone installer here, it should show up on your desktop. Double click on it to open the installer, and follow the prompts.
http://support.apple.com/kb/DL1626
SMC update 1.6
You don't say which OSX you are running so I will include the links for those installers as well, select only the one that applies to your OSX, and download that one and follow the same installation instructions as above. (it should download to your desktop)
Snow Leopard 10.6.x http://support.apple.com/kb/DL1678
Lion 10.7.x http://support.apple.com/kb/DL1677