In order to deinstall POS PSIM, run the following command in the wmic.exe utility: 

/NODE:"Computer_name" /USER:"User_name" /PASSWORD:"Password" product where name="Product_name" call uninstall

Here Product_name is the name under which POS PSIM is installed, usually POS PSIM v.Build_number. The name can be found in the registry in HKEY_LOCAL_ MACHINE\Software\Microsoft \Windows\CurrentVersion\Uninstall section.