To start restart the computer the folder was indeed occupied by some process and restart will solve this problem.

Also check if you've installed in this folder, any program that you are working with, and that is running, and check the folder data encryption. Also the folder should not be in the name of the system folder.
Don't forget to do a routine virus scan — some viruses block folders and files and protect them from deletion.
If all the above steps have not led to success, open the folder with the file that is not deleted. Go to folder options in the "tools" section and open the tab "View". Check whether there is tick on the "to Use simple General access to files". If it is — uncheck it, click OK and close properties. Then click on the file, right-click and invoke properties. In the "Security" tab, open "Advanced" and uncheck all boxes in the areas of reading and performance. Now try to delete locked file.
Also, you can help a good Explorer, Total Commander, showing the locked files and folders. If you found the encrypted file, press Ctrl+Alt+Delete and in the processes view, if there is something that matches the name of the blocked file. If the process is found, stop it and delete the file.
If these methods don't lead, use the latest and the most reliable way of deleting folders and files — download and install the program Unlocker. This program will allow you to delete even locked files and folders and also rename them, move and Soviet other operations. After you install the program, then right-click the folder or file that you wish to remove. You will see in the context menu that appears Unlocker — click it, unlock the file to the opened window and remove it.