It is currently not an option to change the icon size. However, with so many people now adopting these super high resolution monitors, I am currently in the process of converting all the bitmap style icons into scalable icons. When I'm done, you'll be able to set your icon height to any size you want. Here's an example of the current 24 x 24 pixel seatpost clamp icon and the new seatpost clamp icon set to a height of 150 pixels.

In the meantime, I've been pointing out that there is some other functionality in BikeCAD that makes it so you don't even have to use the icons. For example: bikecad.ca/ease_of_use_improvements_version_10.

The GUI text can also be made larger as described at: bikecad.ca/changing_gui_font.