The process you're trying to do is related to changing the metadata of files. Once you modify a picture, a new date will be assigned to it in the Metadata field. Unfortunately, Lenovo Photo Master doesn't give you the option of changing the metadata of the loaded images. You will need another application for this procedure. Luckily, there are plenty available for this operation.
Use the database of Software Informer to look for these apps: http://software.informer.com/search/change+image+metadata