In order to change the odds type in the mobile version, all you have to do is click "My Bets" at the bottom of the screen which will open a new menu. At the top of this menu, you will see the gear icon which allows you to change your odds settings. In case you are using the PC version, click on the gear icon found on your bet-slip next to ‘My Bets’ near the top-right of the screen.
Once you click the gear icon, this will open up a small menu with ‘Odds Type’ showing at the top, which is where you can choose between three formats for the display of your odds - Decimal, Fractional or American as in the following example: