How do I download ios14

You provide no information as to your iPad model - or the currently installed version of iOS/iPadOS.

Whether you are able to update your iPad to a newer version of iOS/iPadOS will be dictated by your iPad model - and the currently installed version of iOS. You can find this information here:

Settings > General > About

Not sure which iPad you have? Identify your iPad model.

Here is a list of the highest version of iOS supported by the older models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:

iPad1 - iOS 5.1.1

iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi & Cellular)

iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi & Cellular)

iPad Air1, iPad mini2 and iPad mini3 - iOS 12.4.9

Newer models, not appearing in this list, are all able to be updated to the current version, iPadOS 14.2.

Of your iPad is capable of being updated to a more recent version of iOS/iPadOS than is currently installed, this support page describes the available methods by which you can update:

Update your iPhone, iPad or iPod touch – Apple Support