Imagine the difficulty of running a conspiracy to change Biblical texts. You'd have to find and modify every copy of scripture everywhere on the planet. The only people who realistically could've attempted this might've been a Roman Emperor or an early corrupt Pope.
But even those people wouldn't have been unable to modify the Dead Sea Scrolls, as those weren't discovered until well after the Roman empire ended / Papal authority of all Christians faded. There are also many other ancient manuscripts, some discovered relatively recently (i.e post reformation) and a couple dating back into the first millennium BCE [1].
Spoiler alert: there are some differences, but many more similarities.