Post in ascending order?

I have a blog on wordpress.com that I wold love to have the post in ascending order, it is a diary of sorts, so I would love to have Day 1, Day 2, Day 3, etc with Day 1 alswasy at the top?

I believe there are themes for self hosted wordpress sites that can do this, and if I have to I will cponvert it to a self hosting blog, but I am hoping there is a free wordpress.com way to achieve this?

Thanks very much

Henry