Installing them is similar to installing a patch.
If you already have Fractal-Bot installed, and you click on the *.syx file, it should open the Fractal-Bot automatically. Once this is open, click on the speaker you wish to install, in the "Browse" button space, and it will be setup, ready to install. Then click on the "Begin" button, and another box will open, asking you which location you wish to install it in. It will give you the option of 1 through 100, which are the User Cab slots; type in the slot you wish to save it, and click "Send". This will take about 2-seconds, or so, and the new cab is installed in your AxeFX unit.
To access the new cab click on the Cab block (if you're using Axe-Edit), and go to the User cabs; the cab will be in the user cab slot you installed it in. You may need to refresh your Axe-Edit cabs, by clicking "Settings", "Preferences", "Refresh", "Cab Names", if the new cab doesn't show up in Axe-Edit. Once you've done this, it's also installed in Axe-Edit, as well as in your AFX unit. To use it in Axe-Edit click on cabs, and select Hi/Ultra, and the cab you wish to use.
From my end, I'm REALLY digging the new hi-res cabs. I plunked down my nickle, and bought the entire OH collection - they're really good.