I have an old iPhone 1 and it's iOS is way out of date. I can't figure out how to update my iOS?

My iPhone 1 needs an iOS update but the Software Update tab isn't in my settings (Settings>>General>>Software Update) and I can't figure out how else to update it. Can someone with computer/iPhone/technology experience help me please?

It's impossible to update iPhone 1 to iOS 8. I think your phone would probably explode. The phone can't handle the requirements for the newest iOS

The highest ios version the original iPhone 1 can use is iPhone OS 3.1.3. If that is your current version of ios, there's no way of updating your iPhone past that. This is how Apple makes people buy newer models, by making older models incompatible.