If you would like to remove multiple galleries at one time you can follow the steps below.
From the main menu click on Photos » Galleries.
Make sure your galleries are shown in a list by clicking on the List View box in the upper right corner.
Check the box next to each of the galleries you want to remove.
Click the Actions box in the upper right corner.
Click Delete Gallery.
This option will allow you to delete up to 10 galleries at once.