Deleting files from the External drive to free space

I have a My Passport 1TB USB 2.0 external portable drive that I am using with my Mac Book Pro. It is formatted as Mac Extended (Journaled), and I had been using it to back up pictures, and also as a Time Machine backup. Recently I tried backing up more pictures but ran out of space. I bought another external drive, and have now started using that for my laptop Time Machine backups, with the intention of keeping the old one for pictures etc. I deleted the old backup directory on the old drive, but the info menu still shows that it only has a small amount of free space, even tho the files are gone from the directory. I know my picture/video files only take up about 480 GB, but the drive info panel is still showing a couple of GB free. Any clues what I might need to do to free space?

It could be a display error. Does the hard drive show the same space when connected to another computer? If so, try running a disk repair within Disk Utility in case there’s a file system error.

I have just figured this out. When I was dragging the files from the external drive, I was not clearing out my trash until after disconnecting the drive. Therefore the old deleted files were still on the drive, just not appearing in the directory. When I cleared out my trash bin with the drive connected, the space appeared. It did take quite a long time to clear, as there were over 500k files in my old backups! All good now tho thanks!