That is the stock bow roller. It is bolted with nylon locknuts from below. access is through the anchor locker hatch. You're going to need to essentially be inside of the bow pulpit. It is VERY, VERY awkward.
When I replaced mine, I had to put tools, washers and nuts in one hand then lead with that arm out in front first. I couldn't get my arm in and out without crawling bck out a bit . I couldn't get two arms in there at all. it's very tight.