Dragging them to the trash is the right way and then empty the trash to permanently delete them.
If you can't drag the files to the trash, you perhaps don't have permission to do so. Click on the file and then hit CMD-I to bring up the info panel. At the bottom, you should see what kind of permission you have, and you should ensure you have "Read & Write" permissions to delete files..
Before you go and delete anything..... what are you trying to delete?
I'd hate to see a post about how you deleted a system file, or something else that you shouldn't have, and that your Mac is no longer working!
I've created a number of files - in excel, word, as well as photos, etc. that I no longer need on the iMac. Simple files that I have created and cannot seem to delete them.
Also, do you have the red circle/slash (is that redundant?) at the top of the window? (in the toolbar) You can highlight a file, then click that delete button to move things to the Trash. Then it needs to be emptied.
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