Go to Components/BP Gallery/Images. Click on Options button in upper right corner. Then click on Category tab.

Depending on what layout you are using there are 2 settings you should be interested in:

  • For Masonry layout change Columns parameter in Masonry view settings section.
  • For Square layout change Images in row parameter of Square view settings section.
  • For Default layout you can't really limit the number of images per row. It fits as many images as can be displayed in current window with.

You can also change those settings in the Category tab of the menu item you want to have different columns number.