How do you scale down supports?
Right click your mouse and choose Labels which will bring up the Diagrams dialog box. Go to Scales and use the option as marked in the figure below. Reduce the value appropriately and click on Apply > OK.
Occasionally you may run into issues of support icons being displayed so large that they are covering a significant part of the display. If adjusting the scale does not help, try closing out of the STAAD.Pro model and reopening the model back as it could be due to a refresh issue.