How do I clear RAM memory of my iPad 6th Gen?

Restart your iPad: Restart your iPad - Apple Support

RAM is dynamically controlled by iOS.

Your best bet is to leave it alone and let the OS do it’s thing.

Interfering with it can cause your iPad to experience slow downs and issues.

As asked by the others, why do you think you need to clear the RAM?

Do you have a specific problem or issue with which you need assistance?

While a forced-restart will clear temporary caches, it will not fully clear RAM - as some caches will be reloaded upon restart.

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.