This is because the carousel style is set to randomize.
To change this, find the style you are using on the page, go to onMessage > Website > Site Name
- In Pages & Menus find the page you need to change the photo order on
- Click the Edit Wrench
- Click Edit Style
- Click the carousel picture, on the left in the Applied Style dropdown menu, it will show you the style used on this page, as shown below.
- Go back to Pages & Menus
- Click the Styles tab located horizontally at the top of the page
- Search for the name of the Style, then select Copy to copy the style and make the changes in Steps 4-9
- Click the copied Style
- Click Edit
- Click the Gear Icon to the left of the screen
- Click Edit Settings
- Click Randomize Off as shown here
- Save & Close
This change will stop the photos from being show in a random order and go in the order you have selected based on their order in the photo category itself.