I have had a message that updates available but I cannot update my iPhone

What or which error do you see on your screen when you attempt to update your iPhone? Your iPhone 6 can only be updated to iOS version 12.5.5. If you already have iOS 12.5.5 installed on your iPhone 6 then that is as far as the iPhone 6 can be updated. If you have not updated to iOS 12.5.5 and have a notification in settings that there is an update available, then:

Make sure that each point listed below applies to your iPhone before you attempt to update the iOS version-

• Your iPhone must have a fast Wi-Fi connection; you cannot update over cellular data or a cellular hotspot
• The iPhone can not be in Low Power mode
• The battery state of charge must be above 50%
• Your iPhone must have at least 6GB or more free storage space
• Your iPhone cannot be connected through VPN
• You should leave the phone plugged in until it finishes updating, both to assure that it remains above 50% and to keep Wi-Fi enabled (Wi-Fi turns off when the phone sleeps if not connected to power).

Axel F.

iPhone 6 cannot update past iOS 12.5.5.

If you want to update iOS further, you need to buy a newer iPhone model.