CONCEPT
There is a technique to change a file name or rename file.
The logic to rename file is that old file is changed with new file with new name. and new file replace the old file. File constuctor should have the complete path with file name. renameTo() is the command to change the old file name to new file name.
Syntax
 File newfile= new File("C:/Users/vishaldixit/Desktop/"+"newfile_name.jpg");

oldfile.renameTo(newfile);

File oldfile = new File("C:/Users/vishaldixit/Desktop/"+"odlfile_name.jpg");


See other programs in gwt which is required in any gwt project.