The percentage of your window openings that comprise of glazing vs window frames can be set in your Building properties.
To change this, right click on Building in the project tree and select Properties.
Scroll down to Dimensions and edit Window area as shown below.
The fraction of window area occupied by glass defines the amount of glass in the gross area specified for the window. This enables a correction for frame to be made in some heat gain calculation methods.
Note that the U-factor for any glazing, as defined in the Table of glazing should reflect the composite glass and frame performance.