You will NOT lose your clients files.

Close ProSeries and use Windows Add/Remove Programs

Find ProWin 20XX and click Uninstall. It will act like its going to uninstall the entire program, dont panic, it wont! It will open another window that lets you choose which part to uninstall. Find module and uninstall it.

Now restart the computer, and start Proseries back up and Log in, go to Install > Download New Products and make sure that the box is checked for the module you want to install, click Next.