Try this:
1. Right-click on 'My Computer' on desktop
2. Click 'Device Manager'
3. Expand 'Ports (COM & LPT)'
4. Look for something that refers to 'USB to Serial Comm' or similar, and right-click on it
5. Select Properties
6. Select tab 'Port Settings'
I have a
BU-353 GPS puck that came with the Prolific USB to Serial driver. This is the technique I use to change the speed.
Good luck. YMMV.
Rick