Baseline info: https://support-portal.plarium.com/en/throne-web/faq/orders/joining-order 

If you go all the way to the bottom of that, you will see the graphic of a sample order roster.

If you click on the icon of a member, you will see the large graphic of their details. If you are the Master or a Counselor and click in the blank area to the right of the icon, you will get a different window, that includes 'Change Rank'.

From the above link, if you click 'Helping allied Lords' under topics at the top right, you get taken to https://support-portal.plarium.com/en/throne-web/faq/orders/helping-lords  . The 2nd graphic down shows an example of the red 'Change Rank' button.