sir i want to update my old version ioS 11.7.6 version
ioS 11.7.6 version
iPhone 7 Plus, iOS 15
Question marked as
The iPhone 7 Plus can be updated to the latest release of iOS 15.
Please see: Update iOS on iPhone - Apple Support
Update iPhone manually
At any time, you can check for and install software updates.
Go to Settings 
> General > Software Update.
The screen shows the currently installed version of iOS and whether an update is available.
To turn off automatic updates, go to Settings > General > Software Update > Automatic Updates.