How to modify the font size of a document from code

How can the parts of the document be discovered and the fontsize changed?

Here is a sample table used,

RunProperties runprop = new RunProperties();
                Run run = new Run();
                Run run2 = new Run();
                FontSize fonz = new FontSize();
                RunProperties runprop2 = new RunProperties();
                RunFonts runf = new RunFonts();

                foreach (DocumentFormat.OpenXml.Wordprocessing.TableRow tableRow in table.Descendants<DocumentFormat.OpenXml.Wordprocessing.TableRow>())
                {
                    i++;
                    foreach (DocumentFormat.OpenXml.Wordprocessing.TableCell tableCell in tableRow.Descendants<DocumentFormat.OpenXml.Wordprocessing.TableCell>())
                    {
                        j++;
                        DocumentFormat.OpenXml.Wordprocessing.Paragraph para = tableCell.GetFirstChild<DocumentFormat.OpenXml.Wordprocessing.Paragraph>();
                        run = para.GetFirstChild<Run>();

                        if (run != null)
                        {
                           // run or para, both have the same result
                            fonz =  run.Descendants<DocumentFormat.OpenXml.Wordprocessing.FontSize>().FirstOrDefault();
                            fonz.Val = "6";
                        }
					}
				}

Here if this code runs, the text outside of the content controls is changed to '6' fontsize.  but the top part is only content control and the bottom is label + content control.   The label here is "Salesman name:" and "Another textbox"

Using the above reference the fontsize of this can be changed, but the text inside the sdt's is not touched

How are these parts 'addressed' to be able to change the properties?