ashleyfd, I think the only way is to change the date and time of the post, but it’s a fiddle. I notice quite a few forum posts asking for this feature on posts, comments etc and I put it up as a development idea in the “ideas” section yesterday.
@ashleyfd, the newest posts do always appear on top. The only way this can be changed is if you have marked posts as ‘sticky’. But without a link to your blog it is impossible to tell whether this has happened.
As rosclarke says, posts show up from newest to oldest – that’s the way blogs work. Your two posts have the same date, so the one on top was published at a later TIME the same day. You can change that time to reverse the position of the posts (post editor, below the sticky option).