Clearing the InfoPath Cache
When you load an InfoPath form, it is cached in the following location on your machine:
C:\Documents and Settings\[User]\Local Settings\Application Data\Microsoft\InfoPath\FormCache2
When a new version of the form is detected, such as when a new version of the form is installed in a SharePoint Forms library, the cached form will be deleted and the new one installed in it's place.
You can also manually clear the Infopath cache by deleting the files.
Or you can do it via command line by:
Start > run > Infopath /cache clearall