Erase disk

I have a 500GB external drive linked to an imac. I used it initially for Time Machine backups but have now switched to Time Capsule. I want to clean it off. I deleted the files that I could see on the drive in Finder but although nothing is visible, it is showing only 95GB free. How can I clean it down completely?

Thanks McBie - that's done the trick. Much appreciated.

connect the external disk you want to clean
Launch diskutility.app from the applications-> Utility folder
Select the disk you want to clean in the left hand pane
Erase the disk

Make sure you select the correct disk and think twice before you confirm the erase action.

Cheers ... McBie

No worries mate, happy to help.

Cheers ... McBie