If we could clone them like in Jurassic World, using foreign DNA, then we could possibly make them bigger, possibly big enough for riding. BUT, you would have to tame one first, and even if you could tame one, they probably would outsmart any attempt to cage them. Now if you could "edit" their brains to make them dependent on instinct once we tame them they probably would be like a horse, just on two legs and with all the problems that ensues.
After you tame them you would need to think about how you will ride it, with a saddle or bareback. Now if you wanted a saddle, you would have to come up with a design that would fit both rider and animal, and not be too overly uncomfortable to both. You would also have to think about the way the animal moves and how the rider would have to move to stay on.
The best possible saddle for a raptor would probably be the ARK: Survival Evolved raptor saddle, found via Google here: https://www.google.com/search?hl=en&site=imghp&tbm=isch&source=hp&biw=1366&bih=667&q=ark+survival+evolved+raptor+saddle&oq=ark+survival+evolved+raptor+saddle&gs_l=img.3..0i30k1j0i24k1l2.1143.12758.0.12943.34.14.0.20.20.0.231.1535.9j0j4.13.0....0...1ac.1.64.img..1.33.1549...0.SdrGJCS2jhQ#imgrc=SPdQLWAKhWf8tM%3A (dang that’s long...)here:
Now, how the rider moves is crucial to not getting thrown off. The most efficient way to ride a raptor at full run (In my opinion) would be to jockey it like a racehorse. For riding at a walking pace, the most efficient way would be to flex the lower half of your body to match the movements of the raptor, like flexing your body when jumping with a horse.