I think it's pretty clear: they want you to decrease, that is, make the stitches fewer, and the rows shorter. Or increase etc.... Using a different one from theirs will not change the shape of the item. If they don't specify, they probably don't care which, or are allowing room for you to decide yourself. If you want eyelets, increase with yos. If you like being able to count your decreases or want them visible to a close examination, use kfb. If you want the least visible decreases, choose those you consider least visible. If you can only do k2tog, use that. If you want them mirrored, mirror them... which do you prefer?