You can configure the web browser of your iOS device to remember form data, usernames and password, by enabling the Autofill feature (Settings > Safari > AutoFill).
It is a useful feature, but in some situations it may be required to clear all your private information. The procedure is explained below:
- Go to Settings > Safari > Autofill.
- Tap on the Clear All button.
- Tap on "Clear AutoFill Data" to confirm.