Hello ohu812, thank you for being a part of the Samsung Community. I understand your concerns about your device slowing down to 4G after the recent update.
Make sure you verify your account is in good standing and service is active with your carrier. Some carriers may slow data access once you have reached a certain limit, or data may be slower in certain areas. You would need to contact your Carrier for further information.
You can try resetting your Network Settings: Navigate to and open Settings. Tap General management, and then tap Reset
Tap Reset mobile network settings for issues with your mobile connection, or Reset Wi-Fi and Bluetooth settings and then tap Reset settings. You may be prompted to enter your security credentials. Tap Reset to finish.
