Default Help Updating (Sorry for noob question)

hey guys have been out of the modding life for a long time now since HTC Amaze came out on market and ive had nexus' (galaxy nexus) since then. i had a quick question. my sister passed down to me a S3 T-Mobile one. its on 4.1.1 and i had at the time put in CWM long time ago as i was gonna flash custom roms but never got around to it (i did this with the help of a youtube video.) now i have this device the Volume UP button doesnt work which is essential to go into download mode... how would i go about updating this to the latest 4.3 Firmware? if there are any detailed steps id really appreciate them. Sorry i know it sucks to get noob posts like these but i have done a bit of research and i cant seem to ask the right questions on google! thanks


btw just for though im switching from nexus 4 to s3 just cause i dont need the power from the n4 and i just want the s3 screen
Samsung Galaxy Nexus - Stock 4.0.1 Ice Cream Sandwich - Screen Protector - Case Mate Barley There Case - 16GB