Open the document whose style set needs to be modified, then open the Word Options dialog box, select the quick access toolbar option on the left, select the command option that is not available in the ribbon in the drop-down list on the right, select the change style option in the list box below, and then click the Add button to add it to the list on the right. After setting, click OK to close the dialog box.
Click the "Change Style" button in the quick access toolbar, select the "Reset to Default Style Set" option in the open list, and then select the style set that the document needs to use in the open cascading list. At this point, the selected style set will be loaded into the list of style libraries in the style group, and the document format will be changed to the style of the style set.
Click the Change Style button in the Quick Access toolbar, select the Paragraph Spacing option in the drop-down list, and then select the desired paragraph spacing in the open cascading list. At this point, the paragraph spacing in the document will change to the selected value.