Ryan will most likely be echoing his full titan shifting (is that Tier 2, I wonder?). It'll basically look like he does now but 15m tall and, oh yeah it's a Titan. However unlike Eren, Reiner has never shown signs of being unable to control his titan form (even at age 10-11) so he's going to be in full control of this giant creature that can punch through walls, etc.

Unlike Reiner (or well, closer to how he is later on...?) Ryan will be using his power to protect people, and his shifting will likely trigger from trying to protect Bertholdt. (OH THE CANON PARALLELS.) I need to hit up nor to confirm if that's all okay BUT basically a 15m titan is in Ryan's future, the fortunate side-effect to that will be that when he shifts back, he'll no longer look like the Armored Titan. (That appearance might come back later, though... Anything's possible.}