Before you create the graphs, go to Statstica menu "File > Options > Documents > Graphs > Settings", and set the option "Scaling of fonts/markers".
The default is 100%.
An example histogram below is generated with default 100% scaling.
After changing the font scaling option to 200%, regenerate the same graph, and it is as below with enlarged text fonts for titles, legends, axis labels.
Users can flexibly adjust the font scaling option as needed.