Hi.,
Thank you for contacting us.
1) Kindly refer the attached video : http://recordit.co/YRhxbIi9Of
2)Get into Admin Panel > Appearance > Customize > Additional CSS > Paste the below css code inside the text area > Save All.
#dt-1505559553043-0fc3b635-35b1 ul.dt-primary-nav > li > a { font-size: 16px !important; }
If you still have any issues, kindly send us some screenshot/video where you have the issue. So that we will check the issue.