If you see the error shown in Figure 1 when you try to update or install PSTC, you'll need to remove the existing version via the control panel. While this may be tedious to perform an update, this is the current workaround for the error.
Figure 1 - PSTC Install Error Message
First, open the control panel and click "Uninstall a program" under the Programs heading, as shown in Figure 2.
Figure 2 - Control Panel Window
Secondly, select "PSTC for GRL3 + GR2A v3" from the list of programs, and click the "Uninstall/Change" button in the toolbar. See Figure 3.
Figure 3 - Installed Program List
Finally, select "Remove the application from this computer" and click OK as shown in Figure 4.
Figure 4 - PSTC for GRL3 + GR2A Maintenance dialog