Can I connect to cellular data instead of WiFi?

Hello! Follow these directions from this Apple Support Article.

Disconnect from Wi-Fi networks

Open Control Center on your iPhone or iPod touch, or iPad and tap the Wi-Fi button . The icon dims and your device disconnects from any network that you're connected to.

While Wi-Fi is disabled, auto-join for any nearby Wi-Fi networks is also disabled until:

• You turn on Wi-Fi in Control Center.
• You connect to a Wi-Fi network in Settings > Wi-Fi.
• You walk or drive to a new location. 
• It's 5 AM local time.
• You restart your device.