If a file is deleted from the Folder, it will be placed in the Trash can, from where it can be restored. 

Thhose files that are deleted from the Folder are placed in the Trash can. The files in the Trash can are automatically deleted after a certain amount of time, so there is no need to spearately delete them. The files stored in the Trash can do not count in the users' quota. 

Files can be deleted two ways; if you only want to delete one file, right-click on it, and choose 'Delete'. 

If you want to delete multiple files, select them (you can select multiple files by clickign on the icon next to them or in the empty field next to the file name) and choose 'Delete selected' in the left side menu. 

Files that are in the Trash can can be restored. To do this, enter the Trash can, select the files to be restored and choose 'Restore' on the left.