Yeah it wasn’t so much that as it was, “when the heck did they have TIME to do it?” They were in a mad rush to find and retrieve the data file while K-2 was simultaneously helping them search and fending off wave after wave of troopers. At least for Luke and co. it happens in a moment of relative downtime when they aren’t actively running from troops.
It’s not a big deal, just a funny little observation.
Heres my take, I think they did it to lighten their load because they knew they were about to be climbing and felt more comfortable in their lighter weight outfits.
My only two gripes, which have been addressed by others here in the forum, were the lack of stormtrooper continuity and Vader’s actor. In the OT, stormtroopers had to be roughly 6’-6’2" and weigh around 180-200. In R1, they were a hodge podge of body types and heights. Hell, there were even some fat troopers. Not a big deal, but an attention to detail SNAFU none the less. But the biggie to me was the actor who played Vader sucked! His gait was wrong, his hip swivel was not a Vader trait, his body type was not Vaderesque. More attention shoulve been paid to who wore the Vader suit. This guy had skinny legs, hyper extended knees, narrow shoulders (maybe it was the shoulder armor), flat chest etc etc. His battle scene movements werent too bad though. Spenccer Wilding, although a big guy like Prowse, had a more slender swimmers build than Prowse. Prowse had a more square body type which gave the appearance of more girth throughout. Oddly enough, Hayden Christianson did a better job in the Vader suit that this guy.