Please launch any Adobe Product installed in your machine and then go to the Help menu.
Click on Help-> Updates and search for ACR 5.7 updates.
Once they are listed , download and install them.
Please revert in case you face any issues.
This is the first thing I did to update and also tried downloading directly from adobe but get the same results.
You can install the plug-in manually.
Go here for Windows: http://www.adobe.com/support/downloads/detail.jsp?ftpID=4681
go here for Mac OS: http://www.adobe.com/support/downloads/detail.jsp?ftpID=4680
to download the plug-in.
Follow the directions at the bottom of each page on how to install. IMPORTANT: the install location is precise. Please follow the instructions carefully!
There can only be one Camera Raw plug-in in the appropriate folder. So remove the one that's already there, or say yes when you're asked to replace the one that's there (if there is one).