I can’t IOS update on my iPhone 6s Plus

What happens when you try?

Can you post a screenshot of the whole screen, it could reveal why you aren't able to update.

Make sure you:

• Are using a WiFi connection (not a hotspot).

• Have your battery charged at least 50%. Better yet, keep it plugged in during the update.

• Are not using a VPN connection.

• Do not have power save mode turned on.

• Do not have a beta version installed.

• You have at least 6 gigs of storage available.

You can also check out this article for help -

If your iPhone, iPad or iPod touch won’t update

https://support.apple.com/en-gb/HT201435

You will probably need to use iTunes to complete the update.

Update your iPhone, iPad, or iPod touch with iTunes - Apple Support (CA)

Note: the update will be to iOS 15.1.

What is the existing version of iOS on the device?