@Leir: That's a valid concern
. The update is pretty massive, and, if your PW is WiFi only, the factory reset will kill the registration & wifi settings, so, no wireless, (and even if it's 3G, I don't think you're likely to get it, especially given its size. Regardless, switch to airplane mode ASAP to be safe), but better check that it's not waiting in the wings on the USB drive before proceeding.
(FYI, the factory reset is accessible in the Settings' menu).
Another solution would be to follow the 'safe' 5.3.0 update instructions (cf. the JailBreak's Bridge section) first.