To completely remove all the unnecessary files, use the Total Commander. The program is not free, but it has a long trial period in a month, then it is possible to continue to use, but you need to press the button with the specified number when the program starts. As part of this program, there is a good FTP-client. It allows you to manage the data that are on the server, ie, we can remove unnecessary files.
After starting the program, press the key combination Ctrl + F or click the menu FTP, then "Connect to FTP-server." In the next window, click "Connect" if connection data have been entered in advance. Otherwise, click "Add" and enter the data for the connection to the server. After a successful connection to the server, navigate to the folder with the pictures, the default - wp-content / upload.
This folder contains many files, many can be removed. To do this, click the menu "Selection", then "Select group". You can also press the Num +. By this action, we create a mask to remove the files of the same type. In the "Search for Files" select the symbol x (it is present in the file names). Click "Burn" and then select the name of the template.
After pressing the Num +, select the newly created template. As a result, it will select all files on the specified mask. Check out all the files, did not bring any template files you need. You need only remove the files small size. It remains only to click on the Delete button and wait for the end of the operation.