Is there a way to edit the autofill text?

If you're referring to the keyboard autocorrection, you can delete suggestions from the stored dictionary and prevent them from appearing again by touching the "x" on the suggestion bubble before making any further keyboard entries. The dictionary will also learn your entries and corrections as you type them.

You can turn off auto-correction altogether: Settings > General > Keyboard > Auto-Correction ON/OFF

You can also reset the autocorrection dictionary to default: Settings > General > Reset > Reset Keyboard Dictionary

If you're referring to Safari AutoFill, you can't edit it but can clear the list, or switch off names and passwords.

Settings > Safari AutoFill > Use Contact Info On/Off, My Info, Names & Passwords On/Off, Clear All.