Once a tab stop has been created, it can be changed at any time:
To do so, select the paragraphs whose tab stops you want to edit and open the dialog box via the Tabs icon 
on the ribbon tab Layout | group Paragraph.
Select one of the set tab stops in the list Tabs. The Clear button allows you to remove it. The Clear all button removes all tab stops in the selected paragraphs.
It is not possible to move a tab stop to a new position via the command Tabs . You can only clear the tab stop and then set a new one at the desired position. However, it is easier to move tabs via the ruler.