Well, there's a button near the top left that selects what you do and don't want to see (GC games, Wii games, real NAND, emuNAND ... ) You'll need to uncheck the real NAND first, just to be safe.
you can then go to anything that you're never going to actually run from emuNAND like Wii U menu and WiiFlow, select the channel, go to the settings, go to the uninstall menu (last one ?) and remove it. That should delete it off of your emuNAND.
If you want to do the same thing with real NAND, though, it's a little more complicated since you don't really wanna go deleting something off of your real NAND. What you'd do it create a category (call it "hidden' if you like) and then add to it everything that you don't want to show up. You'd then to to where it tells you which categories to show and you click in it's checkbox a few times until it has an X in the box. That will then hide everything that's in that category.
(unfortunately, I've only seen this process described, haven't actually done it myself so I don't know exactly how to create a category in USBLoader GX ... but I kinda remember seeing something about it, also near the top left. I'd hope it's fairly self explanatory
)
