You have to remove the previous version before installing the new one.

Please note, that for Garmin iQue 3600 to work in landscape, it is necessary to have system update 5.2.1r3. You can download this update from the Garmin web-site.

Preferences panel allows the user to set the per-applications settings
to help resolve possible incompatability. 
The following options are available:

Options related to orientation preferred for the application.
"Default" - application will be started in the current display
orientation.
"Landscape" - application will be started in landscape or reverse
landscape mode depending on the "Trigger Rotation" setting (see below).
"Portrait" - application will be started in portrait mode.
"Auto" - orientation of application depends on the flip cover
position on NX/NZ and UX device. When such a device is in clamshell
mode the application will be started in "native" orientation (portrait
for NX/NZ and landscape for UX). When the device is in tablet mode
the application will be started in landscape for NX/NZ and portrait
in UX.

"PalmSource API" - enables the Pen Input Manager API (present on T|T3,
T|T5, Life Drive and Zodiac) for the application.
"Sony API" - enables Sony-native Virtual Silk API.
In general it is safe to leave the default state for these options
(i.e. both enabled). But if you are experiencing a problem with the particular
application,  try to disable one of these APIs for the application. When both
checkboxex are disabled, the app will work only in 320x320 mode. 

"Locked" - disable rotation for this application. Useful for applications
that work well only in one specific orientation.

Preferences panel also has a menu bar with the following options:

"Trigger..." will popup a dialog with the rotation trigger settings.
Trigger could be totally disabled by choosing the "None" option.
It is also possible to set the rotation angle:
"Left" - trigger will rotate the display to 90 degrees counter-clockwise.
"Right" - trigger will rotate the display to 90 degrees clockwise.
"Both" - only for TH/NX/NZ device. Trigger will rotate the display
as in Landscape 1.0.

"Uninstall..." will remove the system extension (RotationMgr). You'll have to remove a panel manually.