i need to update my iphone plus 6, please help me?

if you check your iPhone model in Settings > General > About, what does it say?

What iOS version are you currently running?

your post says you have an iPhone 6 Plus, but your details say you have an iPhone 6s Plus.

If you have the 6s Plus, you can update to iOS 14, if you have the iPhone 6 Plus, you can update to iOS 12.4.9

Update your iPhone, iPad, or iPod touch - Apple Support

Updating iOS: common issues and solutions - Apple Community