Where it's located is device-dependent, for MSM-capable devices it's either in Garmin folder of older models or .System folder of newer. There's only need to delete it, if present, before updating manually by RGN or with GCD on media card. Other 'conventional' updating done via GarminExpress or WebUpdater will simply overwrite any existing GUPDATE.GCD file as will of course manually copying one to the correct folder in MSM. Leaving it on the device after updating causes no issues if the device doesn't automatically delete it after updating from it.