Anachronisms
Your application may use some display features that are out of place in a modern GUI. For example, many legacy programs display a standard header on every screen which includes the program title, time, date, etc. This may make sense on a dumb terminal, but makes little sense on a PC, where the time and date is available on the status bar. You can move the program title to the title bar of the window, or, after eliminating the superfluous bits, make it stand out by putting it in a large font.
Another example is the traditional AlphaACCOUNTING-style Add/Change/Delete/Print menu which takes a ridiculous amount of display space just to set a mode switch. Better to move right to the editing screen, and if it is necessary to establish an Add/Change/Delete mode, display a row of buttons for that purpose.
After replacing the header and installing a button menu along the bottom, here’s what our screen looks like (OK, the banner isn’t quite right for the application, but you get the idea):
