Shower Alcove Stud adjustment

[Forcomicrelief]

I am preparing a small alcove for a 4 piece Lyons prefab standing showe 32×32 the back wall has some molded in shelving that require the shower studs to have a 20" gap and mine are 16" on center. The stud I need to move appears to have a ceiling or attic joist attached to it. (See pictures)

How do I move this stud? The far right wall is an exterior wall if that matters at all. I'm imagining moving the stud and using 2×4 spacers to reattach the top joist?