To replace already existing package: Inno setup

Hey there,

I have already generated a setup.exe using innosetup and my default directory name is
DefaultDirName=C:\Program Files\abc\xyz so that all the files of this application reside in xyz folder.

Now, I want to install another version of the same application in the same directory, that is in C:\Program Files\abc\xyz
I want all the files in the xyz folder to be overwritten by the latest version and there shouldn't any trace of the older files.

Anybody has any idea on what is to be done?Please suggest!

Many thanks :)

use the ignoreversion flag like this

Source: C:\Documents and Settings\Owner\Desktop\work order\SETUP FILES\unitnumber.txt; DestDir: {app}; Flags: ignoreversion;