How to Uninstall Magento Extension...

The method you use to uninstall Magento depends on how you originally installed it.

Uninstall via Magento Connect
If you installed the extension via Magento Connect, follow these steps to uninstall it:

Log into the Magento Admin Panel
Navigate to System > Magento Connect Manager
Find the Braintree_Payments package and select Uninstall from the drop-down menu
Click Commit Changes
Uninstall manually
If you manually installed the Braintree extension, you’ll need to remove the following files and folders to uninstall it:

/app/code/local/Braintree/Payments
/app/design/adminhtml/default/default/layout/braintree.xml
/app/design/adminhtml/default/default/template/braintree/
/app/design/frontend/base/default/layout/braintree.xml
/app/design/frontend/base/default/template/braintree/
/app/etc/modules/Braintree_Payments.xml
/app/locale/en_US/Braintree_Payments.csv
/js/braintree/
/lib/Braintree.php
/lib/ssl/
/lib/Braintree/
/skin/frontend/base/default/braintree/