Login to the particular server running GPS:
1. Go to windows services (type services.msc in the Run window) or via the Services menu option of the Administrative tools;
2. Select the GPSDisp service;
3. Click Restart;
4. Click Yes (question about restarting other services that depend on the GPSDisp one).
As an alternative and quicker solution you can use the Restart GPS shortcut on Mercdev's desktop of the GPS server.