You wont lose client data, you may have to do a Homebase Database Maintenance once its reinstalled to pull the client files back into Homebase.  I uninstalled the partnership module last week, just reinstalled it yesterday and my clients were all still there.

For WIn10
Right click the Start button > Settings > Apps   scroll down the list to ProSeries 2018, click Uninstall    It will act like its going to uninstall the whole program, dont panic, it wont!   Another window opens with a list of modules to uninstall.  After you uninstall, open ProSeries back up, Update >Select New Products, make sure the 1040 box is checked and update.

I believe for Win7, its under Control Panel > Add/Remove Programs  Uninstall PS18