The 192x192 sprites should work just as they are next to the 160x160. Actually, the Gen 5 species sprites that come with Essentials are 192x192 already, unless you've changed them or you have some non-standard download. In fact, I'm pretty sure a lot of the Gen 4 sprites were reused as bases for the Gen 5 animations, so they just took the exact same image and put it on the 96x96 canvas before animating it more fully. I would just leave them alone, honestly. AFAIK all Essentials devs who use the included sprites do the exact same thing, have the Gen 4 160x160 sprites alongside the Gen 5+ 192x192, and their games look fine.
That said, it's entirely possible to resize them, although because the size you want to change them to isn't exactly half/double/etc. their current size it won't look very good without manual edits. Again, I'd really just use them as they are. But if you'd rather see for yourself or don't mind manually cleaning the sprites up, then take your image editing software and, when you resize the image using whatever "Image Size" dialogue it uses, see if there's an option called something like "Resample Image" that can be set to "Nearest Neighbor". I have Photoshop, so for me I'd open the image, go to Image Size, change the width and height to 160, then leave Resample Image checked but change that setting to Nearest Neighbor. The options may have different names in different software, but as long as you're using something more advanced than Paint--fine for creating pixel art but really not great at image editing like this--there should be a similar set of steps. It won't turn out very well, though.
Alternatively, you could find downloads of all the Gen 5 sprites (including older pokémon) at 192x192, or at the original 96x96 and resize them yourself using the method I described above (because you're outright doubling the size they'll turn out fine), and replace all the Gen 4 sprites with those. But even that seems like unnecessary work to me.
