creating uninstaller

Hi

when i create the ard file using AddOnRegDataGen.exe

in one of the text boxes of the creation form i can specify unistalller exe location.

my question is how can i create an unistaller?

it seems to be needed when i'm installing a newer version of my addon over a previous installed one (the sap application informs me that it can't find the uninstaller)

appreciate the help

Yoav