Tap the menu button (house) then the options (bolt) button - at the top you will see App is highlighted. Tap Delete in the list below it - after a short delay, a list of app files will appear, scroll down to the one you wish to delete, tap the name, tap 'delete' and 'done'
For a more esoteric approach, google for and download a program called 'FileZ' which presents considerably more detailed information about the files in memory.