NOTE: The delete option is NOT available on the Standard Plan, since events on this plan can only have 1 Main Gallery.
Here's how to delete a main gallery:
Open the Main Gallery you'd like to delete - skip this if you're already in the main gallery. Example of a main gallery highlighted below:
Click the Menu button at the top right (purple circle with 3 white lines) to open the "Gallery Menu"
Click "Danger Zone" on the menu list. You might need to scroll down depending on your screen size.
Click the "Delete gallery" button.
Enter "Delete" exactly as shown into the input box - it is case sensitive.
Click the "Yes, Delete" button.