It says I’m connected to WiFi but when I press install on the update it says I’m not connected to the internet

Being connected to a wifi network doesn't necessarily mean that you have Internet access.

Things to do:

Connect your iphone to a different wifi network (borrow one from your friends or go to a public place with wifi & internet facilities). If your iPhone can connect and surf the web, then the problem could be related to your modem-router (try to restart it).

Regards

Giulio