To update clients who installed from an administrative image, first update the administrative image and then configure the clients to reference the new copy of the image.
Run SOLIDWORKS Installation Manager from the Internet so that the correct files are referenced. SOLIDWORKS Installation Manager will redirect itself to do this, or you can run the update directly from the SOLIDWORKS Downloads Web site (http://www.solidworks.com/sw/support/downloads.htm).
Once you have updated the administrative image (which creates a new copy of the image), you can update clients by having them reference the new copy of the administrative image.
If clients referenced the previous version of the administrative image using a mapped drive or a shared directory, you could redefine that mapped drive or shared directory using the location of the updated copy of the administrative image.