In reply to Girmantė.

If you want to change the font size of the text in the INSET statement you can use the textattrs=(size=16).

Example:
proc sgplot data=sashelp.cars;
vbar Type;
inset "Type of Cars" / textattrs=(size=18pt color=Navy);
run;

https://go.documentation.sas.com/?docsetId=grstatproc&docsetTarget=p0hz27ehuzdd6pn0zaic6x52pkav.htm&docsetVersion=9.4&locale=en#p0m2l14t4c3cdun1ciwyfcekvqjr