If they are preinstalled, I am not sure if you can delete them completely and forever, but you can try going to settings --> applications and uninstall them. However they will still be in your account online.
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For the on screen advertisements, this is the subsidy that keeps the price of the tablet so low. You can get rid of these advertisements by speaking with Amazon.com via live chat and requesting them to remove "lock screen advertisements".
If they are preinstalled, I am not sure if you can delete them completely and forever, but you can try going to settings --> applications and uninstall them. However they will still be in your account online.
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