Hello there gawdna,
We see you're looking for assistance with updating your payment method via iTunes, but unable to load the link provided, right?
With the link included in your post, this is loading from our end so if it's not on your end, let's try connecting to a different Wi-Fi network, or disable VPN if you're using one. In addition, check out the following steps, and more information via the following resource for help with updating Apple ID payment methods: Change, add, or remove Apple ID payment methods
Change, add, or remove a payment method
You can edit your payment information in Settings on your iPhone or iPad, or in the App Store on your Mac.
Edit payment methods
If you're still having a problem with this, Contact Apple Support for additional assistance.
Have a great day!