Remove the files you want to keep, then empty the trash. If you're not sure you want to keep them, put them in a folder and investigate them and then trash them (or file them away appropriately as appropriate).
The whole point of Trash and its utility is shown above:
but technically, if you had 10 files in trash, and wanted only to delete numbers 3, 6 and 9; then you could open trash, select the others and drag them to the desktop. Then empty Trash. Then, I suppose, put the others back. But what a waste of time.
Message is: only put in Trash what you want to delete. As pointed out above.