To change the theme of an existing competition, follow the below steps.
Select ASSETS in the left hand column of your LIGR dashboard.
Select the competition that you wish to change the theme of.
At the next window, select THEME.
Then click the red button that displays CHANGE THEME.
Hover your mouse over the theme that you like the look of and select PREVIEW.
Here you can select a different colour combination that most appeals to you and your production.
When happy hit USE THIS THEME.