Can't open iPhone 4.2.1 on desktop please help

[Pja987]

Hi I'm having trouble opening 4.2.1 on my desktop how do u open it in winrar I'm new to this iv only just got my iPhone thanks guys

 

[iGaz]

What is it your trying to do? You don't need winrar to extract the ipsw.

If your simply trying to update/restore your phone it can all be done in iTunes...