If you have GW and you only want to update emunand, you can use a rom that has 9.5 on it, but it will not update any of the network apps (system transfer, browser, eshop, etc). You can check 3dbrew for a list of waht doesn't get updated iirc. If you absolutely HAVE to have those apps updated then yes, your only option is to install sysupdater to your emunand then download an update pack from that iso site. extract all of the cia files to a folder named "updates" on the root of your sd card. boot into gw emunand and then run sysupdater.
It is VERY important that you use sysupdater and not another cia installer like BBM, FBI, or DevMenu. Those three do not always install a cia file if the title already exists, where as sysupdater installs ALL files in the updates folder, regardless of whether the title already exists. If you do use one of the normal cia installers you are highly likely to end up with a Frankenstein firmware installation and such an install has been known to cause problems down the line.