hi, i use Ccleaner program Ccleaner download to clean deleted file and temp files from my computer .
or whn you are deleting file if you hold in the shift key and right click to deleted the files it will give option to remove from hdd and not send to trash bin .
I also suggest what CimmerianX suggested. Eraser Deletes the file and then rewrites it with random data pattern until it is unrecoverable, and it's free.
Deleted files normally are not really deleted. The block that they are saved in are just prepped and marked ready to be overwritten but the original data is still saved. By using a tool such as the one mentioned above, the block where the file was saved will be overwritten by random data ensuring that the original content will be deleted. Any attempt to recover it using recovery softwares will only get the random data that was written on it last.