To install MyGUI/Upgrade.
Run Setup-MyGUI and from the options select the directory of your Mystic BBS.

If you want to UNinstall use ADD REMOVE programs for a clean removal of MyGUI.

NOTE:
None of your BBS files are altered in any way by MyGUI.
For Help, use HELP from the MyGUI menu.
MyGUI requires Mystic v1.12 A47 for the POLL Net option to work