Open Settings
Tap General
Tap VPN & Device Management
Tap VPN
Tap the information icon next to the VPN profile
Tap Delete VPN
Confirm deletion
If the VPN was installed as a configuration profile, go back to VPN & Device Management
Tap the profile
Tap Remove Profile
Enter your passcode if prompted
Confirm removal
If the VPN app is installed, delete the app from the Home Screen or App Library
Restart the iPhone if needed