How to replace one wall???
sorry about the grammar in my last post.
you're in Florida you probably have an orange peel type texture on the walls.
I would skip the j-channel and go for flat taping tight up against the textured walls.
"Here's to hoping you havent made a mess yet"
If you cut your angle clean and straight without ripping the sides that are staying (textured) while removing the one wall. There's still an easier way.
Do the above with the ceiling angle.
Cut your wall angles with a razor knife straight and clean.
hang the drywall as tight as you can get it to the staying walls. if it not perfect tight, pre-fill any gaps. Let dry.
nest step needs to e clean, you can't use painters tape to keep it clean and still get the desired finish..
So cleanly apply all purpose mud down the side of the "new" walls angle..place the tape, flat into the angle, bumpt up against the texture wall. Wipe the tape down tight and clean, looking out for spillage onto the texture wall, clean off any.when the tape drys, coat it, keep it clean watching for spillage again.
this is called flat taping.
this will crack if you dont apply a tiny bead of caulk before priming.
after running the bead of latex caulk wipe it down with a semi soaked rag
leaving a very very thin line of caulk that will hold the angle and look correct.
it's a technique used by finishers to finish up against block walls and fire places