Some apps have an "Un-register" option that lets you remove registation information from that machine, so you can then enter a different one.
I don't think Word lets you do that.
Keep in mind that big apps like Word, or most Adobe products are secretive about their registration-storing system so that their software doesn't get pirated.
You can also just re-install the apps, since most installers for non-shareware apps require you to enter the registration information at install time.
I assume you have a situation like: you bought a laptop pre-loaded with software but want your name to appear?