The PeopleSoft PeopleTools 8.56 Upgrade Home Page (Doc ID 2270700.1) contains a link to directions on how to do this.
This documentation will walk you through the steps needed to perform a PeopleTools-only upgrade to PeopleSoft PeopleTools 8.56 using the PeopleSoft PeopleTools DPKs. Be sure to read this before you start your upgrade, because the process flow is different from the traditional method. This documentation is needed in addition to the regular upgrade documentation, found in Doc 2270700.1, section Upgrade Documentation.
More instructions follow this diagram.
If you need to patch PeopleTools to a higher release than what is delivered in the image,
See PeopleSoft PeopleTools Patches Home Page (Doc ID 2062712.2) / Best Practices tab.