How to update the ios-6.1.3 in downloaded ios file?

I downloaded the ios-6.1.3, but i can't update for my iphone so what can i do for update that ios

Open up iTunes and plug in your iPhone. Then click your phone it the side bar. Then where it says update software, hold shift (or command on Mac) and click that. Explorer (or finder if on Mac) will open up wanting the file. If you know where it is stored, just go there and double click it. I'm unsure of the exact location if you downloaded with iTunes, but I know it's somewhere in appdata (application support for Mac)