iOS update

Whether or not 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 12.5.1

Newer models, not appearing in this list, are all able to be updated to the current version, iPadOS 14.4.

If your iPad is capable of being updated to a more recent version of iOS/iPadOS than is currently installed, these support pages outline both the available methods by which the update can be performed - and troubleshooting should you experience difficulties:

Update your iPhone, iPad or iPod touch – Apple Support

If you can't update or restore your iPhone, iPad or iPod touch – Apple Support

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

iOS update and restore errors – Apple Support

In addition to what LotusPilot correctly suggested, if you find that your iPad is very slow, a newer iOS version is always recommended (also for security patches included in almost every update)), but it's not necessarily the ideal medicine for your device. There are many other factors that can compromise its functioning, for example the available storage space (check Settings> General> iPad Storage ... which should have at least 15-20% of the total capacity of your device available).

If not, consider freeing up some space using the steps provided in this support article (make a full backup in advance):--> How to check the storage on your iPhone, iPad, and iPod touch - Apple Support

Regards

Giulio