: Charge your device to at least 80% to prevent it from shutting down mid-process.

Generally, to update the firmware on a Samsung Galaxy S II (GT-I9100), users can follow these steps:

Connect the Galaxy S2 to a PC via USB and move both downloaded .zip files directly to the root directory of the phone’s internal storage or external SD card.

Updato is another comprehensive archive that often offers faster download speeds than SamMobile for free users.