I have a roof ladder which has bearer brackets every few rungs, which stand it off the roof a few inches. I need to move one of these brackets. I'd like to make sure I remove the bracket without destroying it or the ladder. The bracket is secured to the ladder with what I assume is some kind of rivet (there's nothing sticking out of the opposite side of the ladder). Here's a photo: imgur.com/a/FuAVreC

What kind of rivet is this, and how do I best remove it please? I have a drill and an angle grinder. Ta.