If you want to move the lot to an external HD.....
Highlight the OLD FILE Folder
Right click on it and select Edit -Cut.
Now open the External drive and Edit -Paste.
If you merely want to delete some, you will have to select each in turn and delete or make a list of those you wish to delete
Then with the contents of OLD FILES listed, click on each doomed file holding down Control as you work your way down the list you made.
Then right click on any showing blue and choose Delete