My Touch 4g T mobile Plz help!!?

My t mobile my touch 4g been popping up with its update since new yrs n I'm scared to do it cus I dont want my all apps to delete in I don't no how to restore backup whatever all that is so can anyone tell me what it does n deletes puls my phone is cut right now n always the internete works when its cut but now its not!??!?!, plz no stupid andsers thanks godbles
 
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