For clearing data on your Memory Stick, you can try these fixes below, but pay attention some of them will erase all your data in your Memory Disk, so you are suggested to utilize some professional recovery data software like iBoysoft Data Recovery for Mac to recover and backup your files in the Memory stick.
Fix 1: Delete useless files and empty your Trash. Finder > your Memory Stick drive > Right-click them and choose Move to Trash then open Trash and right-cick anywhere and select Empty Trash.
Fix 2: Use the shortcut to delete files. Select the file on your Memory Stick. Press "Command + Delete" keys to move the selected item to the Trash. Then press "Shift + Command + Delete" to empty the Trash or "Option + Shift + Command + Delete" to empty the Trash without a confirmation dialog.
Fix 3: Recover and backup all data with iBoysoft Data Recovery for Mac then reformat your external hard drive.
- Finder > Applications > Utilities > Disk Utility.
- Select your stick and then click Erase in the toolbar.
- Rename your drive and choose a format then click Erase to start.
Hope you can clear all and avoid the data loss.