How can I update my iPad to iOS 11?

There is no current iPad that can update to iOS 11 sorry. iOS 11 is no longer available for any iPad at all.

If your iPad can update to iOS 11, then it can also update to 12 or even 13. You can only update to the most current version of iOS your device supports, you can't choose what to update to.

If your iPad is running iOS 10.3.3 currently and Settings->General->Software Update states its up to date, then its very likely an iPad 4, and cannot be updated beyond that. Its hardware is simply too old to run a newer iOS versions.

FIrst, let’s identify what model your ipad is

Identify your iPad model - Apple Support

then folks can tell you IF your ipad can be updated to iOS11. All iDevices eventually hit a point where they can no longer be updated because their hardware isnt’ powerful enough to run the newest software. Sadly, the may be the case with your device

If you iPad cannot be updated beyond iOS 10.3.3/4, then you have an iPad4.

Update support for iPad4 formally ended September 2017. The final iOS releases for this model were iOS 10.3.3 (WiFi Only models) and iOS 10.3.4 (WiFi & Cellular). iPad4 cannot be updated to any later major version of iOS as it lacks the minimum hardware requirements needed to run more recent versions.

Many App Developers have also dropped support for older devices and iOS versions preceding iOS12 - and have withdrawn older versions of their Apps from the Apple App Store. Withdrawal of Apps supporting older models of iPad is making their utility and usefulness significantly more limited.

If Apps that you need to use now have higher minimum iOS-version requirements, your only option is to replace your iPad with newer model. Even the basic current iPad model supports current iPadOS 13.x - and has hardware specifications that will vastly outperform your old iPad4.

I hope this information is helpful - if only in clearly stating your current options.