Close SiaPrime completely. Download the latest wallet. Extract the downloaded files in to a new location, or on top of an existing install (when asked to replace or duplicate the files, click replace all).
Find SiaPrime from the system tray (bottom right of taskbar on Windows), right click and select ‘Quit SiaPrime’.
If you would prefer SiaPrime to close entirely when closing the main window, edit the ‘config.json’ file from the internal data files and change ‘closeToTray’ to false.