Uhmmm....... Those look like modern, standard flush Allen head crakset chainring bolts to me. You do not want to replace those with regular hex head bolts. if you look in the back you will see the back end of the tubular nuts that retain them. You can use a big coin to engage the slots on them and use an Allen head wrench to remove the bolts at the face of the crank. There should be videos in the net that shows how you remove these bolts. Just do a Google search.