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