Here are instructions from Amazon:
You can remove an app from your Kindle Fire when you’re not using the app anymore.
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From the Home screen, tap Apps.
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Tap the Device tab to view apps that have been downloaded to your device.
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Press and hold the app you'd like to remove, and then tap Remove from Device.
Downloaded apps you remove from your Kindle Fire are stored in your Apps library and can be downloaded again from the Cloud tab.