CANCEL SOFTWARE SUBSCRIPTION

Not entirely sure what you mean. Software Updates (iOS) are free on an iPhone there is no subscription.

If you mean you got a subscription from an App, that enhances the app in some way, then you cancel that by following the steps here:

View, change, or cancel your subscriptions - Apple Support

Go to Settings->Accounts & Passwords->Your email account, and you can edit its settings there.

Why not?

You can tap on the email to edit it.